diff --git a/lib/fluent/plugin/out_file.rb b/lib/fluent/plugin/out_file.rb
index c7033968e9..e4b6ddeaa2 100644
--- a/lib/fluent/plugin/out_file.rb
+++ b/lib/fluent/plugin/out_file.rb
@@ -141,8 +141,8 @@ def configure(conf)
         dummy_record_keys = get_placeholders_keys(@path_template) || ['message']
         dummy_record = Hash[dummy_record_keys.zip(['data'] * dummy_record_keys.size)]
 
-        test_meta1 = metadata_for_test(dummy_tag, Fluent::Engine.now, dummy_record)
-        test_path = extract_placeholders(@path_template, test_meta1)
+        test_chunk1 = chunk_for_test(dummy_tag, Fluent::Engine.now, dummy_record)
+        test_path = extract_placeholders(@path_template, test_chunk1)
         unless ::Fluent::FileUtil.writable_p?(test_path)
           raise Fluent::ConfigError, "out_file: `#{test_path}` is not writable"
         end
@@ -178,7 +178,7 @@ def format(tag, time, record)
     end
 
     def write(chunk)
-      path = extract_placeholders(@path_template, chunk.metadata)
+      path = extract_placeholders(@path_template, chunk)
       FileUtils.mkdir_p File.dirname(path), mode: @dir_perm
 
       writer = case
diff --git a/lib/fluent/plugin/out_secondary_file.rb b/lib/fluent/plugin/out_secondary_file.rb
index b59d531993..f188354dac 100644
--- a/lib/fluent/plugin/out_secondary_file.rb
+++ b/lib/fluent/plugin/out_secondary_file.rb
@@ -71,7 +71,7 @@ def multi_workers_ready?
     end
 
     def write(chunk)
-      path_without_suffix = extract_placeholders(@path_without_suffix, chunk.metadata)
+      path_without_suffix = extract_placeholders(@path_without_suffix, chunk)
       path = generate_path(path_without_suffix)
       FileUtils.mkdir_p File.dirname(path), mode: @dir_perm
 
@@ -106,7 +106,7 @@ def validate_compatible_with_primary_buffer!(path_without_suffix)
         raise Fluent::ConfigError, "out_secondary_file: basename or directory has an incompatible placeholder #{ph}, remove tag placeholder, like `${tag}`, from basename or directory"
       end
 
-      vars = placeholders.reject { |placeholder| placeholder.match(/tag(\[\d+\])?/) }
+      vars = placeholders.reject { |placeholder| placeholder.match(/tag(\[\d+\])?/) || (placeholder == 'chunk_id') }
 
       if ph = vars.find { |v| !@chunk_keys.include?(v) }
         raise Fluent::ConfigError, "out_secondary_file: basename or directory has an incompatible placeholder #{ph}, remove variable placeholder, like `${varname}`, from basename or directory"
diff --git a/lib/fluent/plugin/output.rb b/lib/fluent/plugin/output.rb
index b622720b37..5c19e88b08 100644
--- a/lib/fluent/plugin/output.rb
+++ b/lib/fluent/plugin/output.rb
@@ -39,6 +39,7 @@ class Output < Base
       CHUNK_KEY_PATTERN = /^[-_.@a-zA-Z0-9]+$/
       CHUNK_KEY_PLACEHOLDER_PATTERN = /\$\{[-_.@$a-zA-Z0-9]+\}/
       CHUNK_TAG_PLACEHOLDER_PATTERN = /\$\{(tag(?:\[\d+\])?)\}/
+      CHUNK_ID_PLACEHOLDER_PATTERN = /\$\{chunk_id\}/
 
       CHUNKING_FIELD_WARN_NUM = 4
 
@@ -679,13 +680,27 @@ def get_placeholders_tag(str)
       end
 
       def get_placeholders_keys(str)
-        str.scan(CHUNK_KEY_PLACEHOLDER_PATTERN).map{|ph| ph[2..-2]}.reject{|s| s == "tag"}.sort
+        str.scan(CHUNK_KEY_PLACEHOLDER_PATTERN).map{|ph| ph[2..-2]}.reject{|s| (s == "tag") || (s == 'chunk_id') }.sort
       end
 
       # TODO: optimize this code
-      def extract_placeholders(str, metadata)
+      def extract_placeholders(str, chunk)
+        metadata = if chunk.is_a?(Fluent::Plugin::Buffer::Chunk)
+                     chunk_passed = true
+                     chunk.metadata
+                   else
+                     chunk_passed = false
+                     # For existing plugins. Old plugin passes Chunk.metadata instead of Chunk
+                     chunk
+                   end
         if metadata.empty?
-          str
+          str.sub(CHUNK_ID_PLACEHOLDER_PATTERN) {
+            if chunk_passed
+              dump_unique_id_hex(chunk.unique_id)
+            else
+              log.warn "${chunk_id} is not allowed in this plugin. Pass Chunk instead of metadata in extract_placeholders's 2nd argument"
+            end
+          }
         else
           rvalue = str.dup
           # strftime formatting
@@ -720,7 +735,13 @@ def extract_placeholders(str, metadata)
           if rvalue =~ CHUNK_KEY_PLACEHOLDER_PATTERN
             log.warn "chunk key placeholder '#{$1}' not replaced. template:#{str}"
           end
-          rvalue
+          rvalue.sub(CHUNK_ID_PLACEHOLDER_PATTERN) {
+            if chunk_passed
+              dump_unique_id_hex(chunk.unique_id)
+            else
+              log.warn "${chunk_id} is not allowed in this plugin. Pass Chunk instead of metadata in extract_placeholders's 2nd argument"
+            end
+          }
         end
       end
 
@@ -801,6 +822,13 @@ def metadata(tag, time, record)
         end
       end
 
+      def chunk_for_test(tag, time, record)
+        require 'fluent/plugin/buffer/memory_chunk'
+
+        m = metadata_for_test(tag, time, record)
+        Fluent::Plugin::Buffer::MemoryChunk.new(m)
+      end
+
       def metadata_for_test(tag, time, record)
         raise "BUG: #metadata_for_test is available only when no actual metadata exists" unless @buffer.metadata_list.empty?
         m = metadata(tag, time, record)
diff --git a/test/plugin/test_out_file.rb b/test/plugin/test_out_file.rb
index c77fa101e2..f68624effb 100644
--- a/test/plugin/test_out_file.rb
+++ b/test/plugin/test_out_file.rb
@@ -557,6 +557,35 @@ def parse_system(text)
     check_gzipped_result(path, formatted_lines * 3)
   end
 
+  test '${chunk_id}' do
+    time = event_time("2011-01-02 13:14:15 UTC")
+    formatted_lines = %[2011-01-02T13:14:15Z\ttest\t{"a":1}\n] + %[2011-01-02T13:14:15Z\ttest\t{"a":2}\n]
+
+    write_once = ->(){
+      d = create_driver %[
+        path #{TMP_DIR}/out_file_chunk_id_${chunk_id}
+        utc
+        append true
+        <buffer>
+          timekey_use_utc true
+        </buffer>
+      ]
+      d.run(default_tag: 'test'){
+        d.feed(time, {"a"=>1})
+        d.feed(time, {"a"=>2})
+      }
+      d.instance.last_written_path
+    }
+
+    path = write_once.call
+    if File.basename(path) =~ /out_file_chunk_id_([-_.@a-zA-Z0-9].*).20110102.log/
+      unique_id = Fluent::UniqueId.hex(Fluent::UniqueId.generate)
+      assert_equal unique_id.size, $1.size, "chunk_id size is mismatched"
+    else
+      flunk "chunk_id is not included in the path"
+    end
+  end
+
   test 'symlink' do
     omit "Windows doesn't support symlink" if Fluent.windows?
     conf = CONFIG + %[
diff --git a/test/plugin/test_out_secondary_file.rb b/test/plugin/test_out_secondary_file.rb
index 0e06cb9be9..9bd88968d5 100644
--- a/test/plugin/test_out_secondary_file.rb
+++ b/test/plugin/test_out_secondary_file.rb
@@ -260,6 +260,20 @@ def create_chunk(primary, metadata, es)
       assert_equal "#{TMP_DIR}/dump.bin", path
     end
 
+    test 'path with ${chunk_id}' do
+      d = create_driver %[
+        directory #{TMP_DIR}
+        basename out_file_chunk_id_${chunk_id}
+      ]
+      path = d.instance.write(@c)
+      if File.basename(path) =~ /out_file_chunk_id_([-_.@a-zA-Z0-9].*).0/
+        unique_id = Fluent::UniqueId.hex(Fluent::UniqueId.generate)
+        assert_equal unique_id.size, $1.size, "chunk_id size is mismatched"
+      else
+        flunk "chunk_id is not included in the path"
+      end
+    end
+
     data(
       invalid_tag: [/tag/, '${tag}'],
       invalid_tag0: [/tag\[0\]/, '${tag[0]}'],
diff --git a/test/plugin/test_output.rb b/test/plugin/test_output.rb
index 48dde91d3f..22497ed24a 100644
--- a/test/plugin/test_output.rb
+++ b/test/plugin/test_output.rb
@@ -125,6 +125,10 @@ def create_output(type=:full)
   def create_metadata(timekey: nil, tag: nil, variables: nil)
     Fluent::Plugin::Buffer::Metadata.new(timekey, tag, variables)
   end
+  def create_chunk(timekey: nil, tag: nil, variables: nil)
+    m = Fluent::Plugin::Buffer::Metadata.new(timekey, tag, variables)
+    Fluent::Plugin::Buffer::MemoryChunk.new(m)
+  end
   def waiting(seconds)
     begin
       Timeout.timeout(seconds) do
@@ -219,7 +223,9 @@ def waiting(seconds)
       assert @i.terminated?
     end
 
-    test '#extract_placeholders does nothing if chunk key is not specified' do
+    data(:new_api => :chunk,
+         :old_api => :metadata)
+    test '#extract_placeholders does nothing if chunk key is not specified' do |api|
       @i.configure(config_element('ROOT', '', {}, [config_element('buffer', '')]))
       assert !@i.chunk_key_time
       assert !@i.chunk_key_tag
@@ -227,11 +233,17 @@ def waiting(seconds)
       tmpl = "/mypath/%Y/%m/%d/${tag}/${tag[1]}/${tag[2]}/${key1}/${key2}/tail"
       t = event_time('2016-04-11 20:30:00 +0900')
       v = {key1: "value1", key2: "value2"}
-      m = create_metadata(timekey: t, tag: 'fluentd.test.output', variables: v)
-      assert_equal tmpl, @i.extract_placeholders(tmpl, m)
+      c = if api == :chunk
+            create_chunk(timekey: t, tag: 'fluentd.test.output', variables: v)
+          else
+            create_metadata(timekey: t, tag: 'fluentd.test.output', variables: v)
+          end
+      assert_equal tmpl, @i.extract_placeholders(tmpl, c)
     end
 
-    test '#extract_placeholders can extract time if time key and range are configured' do
+    data(:new_api => :chunk,
+         :old_api => :metadata)
+    test '#extract_placeholders can extract time if time key and range are configured' do |api|
       @i.configure(config_element('ROOT', '', {}, [config_element('buffer', 'time', {'timekey' => 60*30, 'timekey_zone' => "+0900"})]))
       assert @i.chunk_key_time
       assert !@i.chunk_key_tag
@@ -239,11 +251,17 @@ def waiting(seconds)
       tmpl = "/mypath/%Y/%m/%d/%H-%M/${tag}/${tag[1]}/${tag[2]}/${key1}/${key2}/tail"
       t = event_time('2016-04-11 20:30:00 +0900')
       v = {key1: "value1", key2: "value2"}
-      m = create_metadata(timekey: t, tag: 'fluentd.test.output', variables: v)
-      assert_equal "/mypath/2016/04/11/20-30/${tag}/${tag[1]}/${tag[2]}/${key1}/${key2}/tail", @i.extract_placeholders(tmpl, m)
+      c = if api == :chunk
+            create_chunk(timekey: t, tag: 'fluentd.test.output', variables: v)
+          else
+            create_metadata(timekey: t, tag: 'fluentd.test.output', variables: v)
+          end
+      assert_equal "/mypath/2016/04/11/20-30/${tag}/${tag[1]}/${tag[2]}/${key1}/${key2}/tail", @i.extract_placeholders(tmpl, c)
     end
 
-    test '#extract_placeholders can extract tag and parts of tag if tag is configured' do
+    data(:new_api => :chunk,
+         :old_api => :metadata)
+    test '#extract_placeholders can extract tag and parts of tag if tag is configured' do |api|
       @i.configure(config_element('ROOT', '', {}, [config_element('buffer', 'tag', {})]))
       assert !@i.chunk_key_time
       assert @i.chunk_key_tag
@@ -251,11 +269,17 @@ def waiting(seconds)
       tmpl = "/mypath/%Y/%m/%d/%H-%M/${tag}/${tag[1]}/${tag[2]}/${key1}/${key2}/tail"
       t = event_time('2016-04-11 20:30:00 +0900')
       v = {key1: "value1", key2: "value2"}
-      m = create_metadata(timekey: t, tag: 'fluentd.test.output', variables: v)
-      assert_equal "/mypath/%Y/%m/%d/%H-%M/fluentd.test.output/test/output/${key1}/${key2}/tail", @i.extract_placeholders(tmpl, m)
+      c = if api == :chunk
+            create_chunk(timekey: t, tag: 'fluentd.test.output', variables: v)
+          else
+            create_metadata(timekey: t, tag: 'fluentd.test.output', variables: v)
+          end
+      assert_equal "/mypath/%Y/%m/%d/%H-%M/fluentd.test.output/test/output/${key1}/${key2}/tail", @i.extract_placeholders(tmpl, c)
     end
 
-    test '#extract_placeholders can extract variables if variables are configured' do
+    data(:new_api => :chunk,
+         :old_api => :metadata)
+    test '#extract_placeholders can extract variables if variables are configured' do |api|
       @i.configure(config_element('ROOT', '', {}, [config_element('buffer', 'key1,key2', {})]))
       assert !@i.chunk_key_time
       assert !@i.chunk_key_tag
@@ -263,11 +287,17 @@ def waiting(seconds)
       tmpl = "/mypath/%Y/%m/%d/%H-%M/${tag}/${tag[1]}/${tag[2]}/${key1}/${key2}/tail"
       t = event_time('2016-04-11 20:30:00 +0900')
       v = {key1: "value1", key2: "value2"}
-      m = create_metadata(timekey: t, tag: 'fluentd.test.output', variables: v)
-      assert_equal "/mypath/%Y/%m/%d/%H-%M/${tag}/${tag[1]}/${tag[2]}/value1/value2/tail", @i.extract_placeholders(tmpl, m)
+      c = if api == :chunk
+            create_chunk(timekey: t, tag: 'fluentd.test.output', variables: v)
+          else
+            create_metadata(timekey: t, tag: 'fluentd.test.output', variables: v)
+          end
+      assert_equal "/mypath/%Y/%m/%d/%H-%M/${tag}/${tag[1]}/${tag[2]}/value1/value2/tail", @i.extract_placeholders(tmpl, c)
     end
 
-    test '#extract_placeholders can extract nested variables if variables are configured with dot notation' do
+    data(:new_api => :chunk,
+         :old_api => :metadata)
+    test '#extract_placeholders can extract nested variables if variables are configured with dot notation' do |api|
       @i.configure(config_element('ROOT', '', {}, [config_element('buffer', 'key,$.nest.key', {})]))
       assert !@i.chunk_key_time
       assert !@i.chunk_key_tag
@@ -275,11 +305,17 @@ def waiting(seconds)
       tmpl = "/mypath/%Y/%m/%d/%H-%M/${tag}/${tag[1]}/${tag[2]}/${key}/${$.nest.key}/tail"
       t = event_time('2016-04-11 20:30:00 +0900')
       v = {:key => "value1", :"$.nest.key" => "value2"}
-      m = create_metadata(timekey: t, tag: 'fluentd.test.output', variables: v)
-      assert_equal "/mypath/%Y/%m/%d/%H-%M/${tag}/${tag[1]}/${tag[2]}/value1/value2/tail", @i.extract_placeholders(tmpl, m)
+      c = if api == :chunk
+            create_chunk(timekey: t, tag: 'fluentd.test.output', variables: v)
+          else
+            create_metadata(timekey: t, tag: 'fluentd.test.output', variables: v)
+          end
+      assert_equal "/mypath/%Y/%m/%d/%H-%M/${tag}/${tag[1]}/${tag[2]}/value1/value2/tail", @i.extract_placeholders(tmpl, c)
     end
 
-    test '#extract_placeholders can extract all chunk keys if configured' do
+    data(:new_api => :chunk,
+         :old_api => :metadata)
+    test '#extract_placeholders can extract all chunk keys if configured' do |api|
       @i.configure(config_element('ROOT', '', {}, [config_element('buffer', 'time,tag,key1,key2', {'timekey' => 60*30, 'timekey_zone' => "+0900"})]))
       assert @i.chunk_key_time
       assert @i.chunk_key_tag
@@ -287,11 +323,17 @@ def waiting(seconds)
       tmpl = "/mypath/%Y/%m/%d/%H-%M/${tag}/${tag[1]}/${tag[2]}/${key1}/${key2}/tail"
       t = event_time('2016-04-11 20:30:00 +0900')
       v = {key1: "value1", key2: "value2"}
-      m = create_metadata(timekey: t, tag: 'fluentd.test.output', variables: v)
-      assert_equal "/mypath/2016/04/11/20-30/fluentd.test.output/test/output/value1/value2/tail", @i.extract_placeholders(tmpl, m)
+      c = if api == :chunk
+            create_chunk(timekey: t, tag: 'fluentd.test.output', variables: v)
+          else
+            create_metadata(timekey: t, tag: 'fluentd.test.output', variables: v)
+          end
+      assert_equal "/mypath/2016/04/11/20-30/fluentd.test.output/test/output/value1/value2/tail", @i.extract_placeholders(tmpl, c)
     end
 
-    test '#extract_placeholders removes out-of-range tag part and unknown variable placeholders' do
+    data(:new_api => :chunk,
+         :old_api => :metadata)
+    test '#extract_placeholders removes out-of-range tag part and unknown variable placeholders' do |api|
       @i.configure(config_element('ROOT', '', {}, [config_element('buffer', 'time,tag,key1,key2', {'timekey' => 60*30, 'timekey_zone' => "+0900"})]))
       assert @i.chunk_key_time
       assert @i.chunk_key_tag
@@ -299,8 +341,23 @@ def waiting(seconds)
       tmpl = "/mypath/%Y/%m/%d/%H-%M/${tag}/${tag[3]}/${tag[4]}/${key3}/${key4}/tail"
       t = event_time('2016-04-11 20:30:00 +0900')
       v = {key1: "value1", key2: "value2"}
+      c = if api == :chunk
+            create_chunk(timekey: t, tag: 'fluentd.test.output', variables: v)
+          else
+            create_metadata(timekey: t, tag: 'fluentd.test.output', variables: v)
+          end
+      assert_equal "/mypath/2016/04/11/20-30/fluentd.test.output/////tail", @i.extract_placeholders(tmpl, c)
+    end
+
+    test '#extract_placeholders logs warn message if metadata is passed for ${chunk_id} placeholder' do
+      @i.configure(config_element('ROOT', '', {}, [config_element('buffer', '')]))
+      tmpl = "/mypath/${chunk_id}/tail"
+      t = event_time('2016-04-11 20:30:00 +0900')
+      v = {key1: "value1", key2: "value2"}
       m = create_metadata(timekey: t, tag: 'fluentd.test.output', variables: v)
-      assert_equal "/mypath/2016/04/11/20-30/fluentd.test.output/////tail", @i.extract_placeholders(tmpl, m)
+      @i.extract_placeholders(tmpl, m)
+      logs = @i.log.out.logs
+      assert { logs.any? { |log| log.include?("${chunk_id} is not allowed in this plugin") } }
     end
 
     sub_test_case '#placeholder_validators' do