diff --git a/.travis.yml b/.travis.yml
index 3dcd289..7d0e6f1 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -6,7 +6,6 @@ rvm:
   - 3.0
   - 2.7
   - 2.6
-  - 2.5
 
 before_install:
   - curl -L https://codeclimate.com/downloads/test-reporter/test-reporter-latest-linux-amd64 > ./cc-test-reporter
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 59a4ce0..d8f7c64 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,11 @@
 # CHANGELOG.md
 
+## v3.2.4
+
+2021-09-04 JST
+
+- required_ruby_version change to `>= 2.6.0` because Ruby 2.5 reaches EOL.
+
 ## v3.2.3
 
 2020-01-03 JST
diff --git a/lib/tee_logger/version.rb b/lib/tee_logger/version.rb
index 2935cfd..5c9474c 100644
--- a/lib/tee_logger/version.rb
+++ b/lib/tee_logger/version.rb
@@ -1,5 +1,5 @@
 # namespace
 module TeeLogger
   # version number
-  VERSION = '3.2.3'.freeze
+  VERSION = '3.2.4'.freeze
 end
diff --git a/tee_logger.gemspec b/tee_logger.gemspec
index 4af4be3..6d92797 100644
--- a/tee_logger.gemspec
+++ b/tee_logger.gemspec
@@ -9,7 +9,7 @@ Gem::Specification.new do |spec|
   spec.authors       = ['k-ta-yamada']
   spec.email         = ['key.luvless@gmail.com']
 
-  spec.required_ruby_version = '>= 2.5.0'
+  spec.required_ruby_version = '>= 2.6.0'
 
   spec.summary       = 'logging to file and standard output.'
   # rubocop:disable Metrics/LineLength