diff --git a/lib/fluent/plugin/output.rb b/lib/fluent/plugin/output.rb
index 3d64839264..0da22cb5bc 100644
--- a/lib/fluent/plugin/output.rb
+++ b/lib/fluent/plugin/output.rb
@@ -304,6 +304,10 @@ def configure(conf)
             raise Fluent::ConfigError, "<buffer ...> argument includes 'time', but timekey is not configured" unless @buffer_config.timekey
             Fluent::Timezone.validate!(@buffer_config.timekey_zone)
             @timekey_zone = @buffer_config.timekey_use_utc ? '+0000' : @buffer_config.timekey_zone
+            @timekey = @buffer_config.timekey
+            @timekey_use_utc = @buffer_config.timekey_use_utc
+            @offset = Fluent::Timezone.utc_offset(@timekey_zone)
+            @calculate_offset = @offset.respond_to?(:call) ? @offset : nil
             @output_time_formatter_cache = {}
           end
 
@@ -803,20 +807,17 @@ def metadata(tag, time, record)
           if !@chunk_key_time && !@chunk_key_tag
             @buffer.metadata()
           elsif @chunk_key_time && @chunk_key_tag
-            time_int = time.to_i
-            timekey = (time_int - (time_int % @buffer_config.timekey)).to_i
+            timekey = calculate_timekey(time)
             @buffer.metadata(timekey: timekey, tag: tag)
           elsif @chunk_key_time
-            time_int = time.to_i
-            timekey = (time_int - (time_int % @buffer_config.timekey)).to_i
+            timekey = calculate_timekey(time)
             @buffer.metadata(timekey: timekey)
           else
             @buffer.metadata(tag: tag)
           end
         else
           timekey = if @chunk_key_time
-                      time_int = time.to_i
-                      (time_int - (time_int % @buffer_config.timekey)).to_i
+                      calculate_timekey(time)
                     else
                       nil
                     end
@@ -825,6 +826,16 @@ def metadata(tag, time, record)
         end
       end
 
+      def calculate_timekey(time)
+        time_int = time.to_i
+        if @timekey_use_utc
+          (time_int - (time_int % @timekey)).to_i
+        else
+          offset = @calculate_offset ? @calculate_offset.call(time) : @offset
+          (time_int - ((time_int + offset)% @timekey)).to_i
+        end
+      end
+
       def chunk_for_test(tag, time, record)
         require 'fluent/plugin/buffer/memory_chunk'
 
diff --git a/lib/fluent/timezone.rb b/lib/fluent/timezone.rb
index bb6fa86893..53a155153b 100644
--- a/lib/fluent/timezone.rb
+++ b/lib/fluent/timezone.rb
@@ -139,5 +139,19 @@ def self.formatter(timezone = nil, format = nil)
 
       return nil
     end
+
+    def self.utc_offset(timezone)
+      return 0 if timezone.nil?
+
+      case timezone
+      when NUMERIC_PATTERN
+        Time.zone_offset(timezone)
+      when NAME_PATTERN
+        tz = TZInfo::Timezone.get(timezone)
+        ->(time) {
+          tz.period_for_utc(time).utc_total_offset
+        }
+      end
+    end
   end
 end
diff --git a/test/plugin/test_out_file.rb b/test/plugin/test_out_file.rb
index 3cc745f751..0ad30add74 100644
--- a/test/plugin/test_out_file.rb
+++ b/test/plugin/test_out_file.rb
@@ -561,6 +561,79 @@ def parse_system(text)
     check_gzipped_result(path, formatted_lines * 3)
   end
 
+  test 'append when JST' do
+    with_timezone(Fluent.windows? ? "JST-9" : "Asia/Tokyo") do
+      time = event_time("2011-01-02 03:14:15+09:00")
+      formatted_lines = %[2011-01-02T03:14:15+09:00\ttest\t{"a":1}\n] + %[2011-01-02T03:14:15+09:00\ttest\t{"a":2}\n]
+
+      write_once = ->(){
+        d = create_driver %[
+          path #{TMP_DIR}/out_file_test
+          compress gz
+          append true
+          <buffer>
+            timekey_use_utc false
+            timekey_zone Asia/Tokyo
+          </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
+      assert_equal "#{TMP_DIR}/out_file_test.20110102.log.gz", path
+      check_gzipped_result(path, formatted_lines)
+
+      path = write_once.call
+      assert_equal "#{TMP_DIR}/out_file_test.20110102.log.gz", path
+      check_gzipped_result(path, formatted_lines * 2)
+
+      path = write_once.call
+      assert_equal "#{TMP_DIR}/out_file_test.20110102.log.gz", path
+      check_gzipped_result(path, formatted_lines * 3)
+    end
+  end
+
+  test 'append when UTC-02 but timekey_zone is +0900' do
+    with_timezone("UTC-02") do # +0200
+      time = event_time("2011-01-02 17:14:15+02:00")
+      formatted_lines = %[2011-01-02T17:14:15+02:00\ttest\t{"a":1}\n] + %[2011-01-02T17:14:15+02:00\ttest\t{"a":2}\n]
+
+      write_once = ->(){
+        d = create_driver %[
+          path #{TMP_DIR}/out_file_test
+          compress gz
+          append true
+          <buffer>
+            timekey_use_utc false
+            timekey_zone +0900
+          </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
+      # Rotated at 2011-01-02 17:00:00+02:00
+      assert_equal "#{TMP_DIR}/out_file_test.20110103.log.gz", path
+      check_gzipped_result(path, formatted_lines)
+
+      path = write_once.call
+      assert_equal "#{TMP_DIR}/out_file_test.20110103.log.gz", path
+      check_gzipped_result(path, formatted_lines * 2)
+
+      path = write_once.call
+      assert_equal "#{TMP_DIR}/out_file_test.20110103.log.gz", path
+      check_gzipped_result(path, formatted_lines * 3)
+    end
+  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]