diff --git a/fluentd.gemspec b/fluentd.gemspec
index cd942d72c1..df8d5c247b 100644
--- a/fluentd.gemspec
+++ b/fluentd.gemspec
@@ -48,4 +48,5 @@ Gem::Specification.new do |gem|
   gem.add_development_dependency("test-unit", ["~> 3.2"])
   gem.add_development_dependency("test-unit-rr", ["~> 1.0"])
   gem.add_development_dependency("oj", [">= 2.14", "< 4"])
+  gem.add_development_dependency("ext_monitor", [">= 0.1.1", "< 0.2"])
 end
diff --git a/lib/fluent/command/cat.rb b/lib/fluent/command/cat.rb
index 97b7bc72b8..e5e865bceb 100644
--- a/lib/fluent/command/cat.rb
+++ b/lib/fluent/command/cat.rb
@@ -101,13 +101,11 @@
   usage $!.to_s
 end
 
-
 require 'thread'
-require 'monitor'
 require 'socket'
 require 'yajl'
 require 'msgpack'
-
+require 'fluent/ext_monitor_require'
 
 class Writer
   include MonitorMixin
diff --git a/lib/fluent/ext_monitor_require.rb b/lib/fluent/ext_monitor_require.rb
new file mode 100644
index 0000000000..5a2cbbb5fd
--- /dev/null
+++ b/lib/fluent/ext_monitor_require.rb
@@ -0,0 +1,28 @@
+#
+# Fluentd
+#
+#    Licensed under the Apache License, Version 2.0 (the "License");
+#    you may not use this file except in compliance with the License.
+#    You may obtain a copy of the License at
+#
+#        http://www.apache.org/licenses/LICENSE-2.0
+#
+#    Unless required by applicable law or agreed to in writing, software
+#    distributed under the License is distributed on an "AS IS" BASIS,
+#    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+#    See the License for the specific language governing permissions and
+#    limitations under the License.
+#
+
+# To avoid duplicated requirements, extract this logic as file.
+
+if Gem::Version.create(RUBY_VERSION) >= Gem::Version.create('2.7.0')
+  require 'monitor'
+else
+  begin
+    # monitor_ext is bundled since ruby 2.7.0
+    require 'ext_monitor'
+  rescue LoadError => _
+    require 'monitor'
+  end
+end
diff --git a/lib/fluent/load.rb b/lib/fluent/load.rb
index 92ea7d12c2..e7d75daf03 100644
--- a/lib/fluent/load.rb
+++ b/lib/fluent/load.rb
@@ -2,7 +2,6 @@
 require 'socket'
 require 'fcntl'
 require 'time'
-require 'monitor'
 require 'stringio'
 require 'fileutils'
 require 'json'
@@ -33,3 +32,4 @@
 require 'fluent/output'
 require 'fluent/filter'
 require 'fluent/match'
+require 'fluent/ext_monitor_require'
diff --git a/lib/fluent/plugin/buffer.rb b/lib/fluent/plugin/buffer.rb
index e69ec51197..20efb0e80c 100644
--- a/lib/fluent/plugin/buffer.rb
+++ b/lib/fluent/plugin/buffer.rb
@@ -17,8 +17,7 @@
 require 'fluent/plugin/base'
 require 'fluent/plugin/owned_by_mixin'
 require 'fluent/unique_id'
-
-require 'monitor'
+require 'fluent/ext_monitor_require'
 
 module Fluent
   module Plugin
diff --git a/lib/fluent/plugin/buffer/chunk.rb b/lib/fluent/plugin/buffer/chunk.rb
index cab45cc91f..a5a6f2d3b1 100644
--- a/lib/fluent/plugin/buffer/chunk.rb
+++ b/lib/fluent/plugin/buffer/chunk.rb
@@ -18,8 +18,8 @@
 require 'fluent/plugin/compressable'
 require 'fluent/unique_id'
 require 'fluent/event'
+require 'fluent/ext_monitor_require'
 
-require 'monitor'
 require 'tempfile'
 require 'zlib'
 
diff --git a/lib/fluent/plugin/output.rb b/lib/fluent/plugin/output.rb
index 2d545fc4a0..2d52eda479 100644
--- a/lib/fluent/plugin/output.rb
+++ b/lib/fluent/plugin/output.rb
@@ -25,9 +25,9 @@
 require 'fluent/timezone'
 require 'fluent/unique_id'
 require 'fluent/clock'
+require 'fluent/ext_monitor_require'
 
 require 'time'
-require 'monitor'
 
 module Fluent
   module Plugin