diff --git a/.circleci/config.yml b/.circleci/config.yml
index b1183a9..7aad0a4 100644
--- a/.circleci/config.yml
+++ b/.circleci/config.yml
@@ -32,10 +32,6 @@ jobs:
       - store_artifacts:
           path: /tmp/test-results
           destination: test-results
-  ruby-23:
-    <<: *build
-    docker:
-      - image: circleci/ruby:2.3
   ruby-24:
     <<: *build
     docker:
@@ -56,7 +52,6 @@ workflows:
   version: 2
   ruby-multi-build:
     jobs:
-      - ruby-23
       - ruby-24
       - ruby-25
       - ruby-26
diff --git a/README.md b/README.md
index 281b855..bd61411 100644
--- a/README.md
+++ b/README.md
@@ -5,7 +5,7 @@
 - [API Documentation](https://api.scnnr.cubki.jp/v1/docs)
 
 ## Supported Ruby versions
-- Ruby 2.3+
+- Ruby 2.4+
 
 ## Installation