diff --git a/Dockerfile b/Dockerfile
deleted file mode 100644
index 7acb5d1..0000000
--- a/Dockerfile
+++ /dev/null
@@ -1,10 +0,0 @@
-FROM ruby:3.1.0-alpine3.15
-
-RUN apk update && \
-    apk upgrade && \
-    apk add bash
-
-COPY entrypoint.sh /entrypoint.sh
-COPY send_message.rb /send_message.rb
-
-ENTRYPOINT ["/entrypoint.sh"]
diff --git a/action.yml b/action.yml
index 99a71a7..e0b5fc8 100644
--- a/action.yml
+++ b/action.yml
@@ -18,10 +18,20 @@ inputs:
     required: true
     description: 'Message to send'
 runs:
-  using: 'docker'
-  image: 'Dockerfile'
-  args:
-    - ${{ inputs.apiToken }}
-    - ${{ inputs.roomId }}
-    - ${{ inputs.title }}
-    - ${{ inputs.message }}
+  using: 'composite'
+  steps:
+    - name: checkout
+      uses: actions/checkout@v3
+      with:
+        fetch-depth: 0
+    - name: set up ruby
+      uses: ruby/setup-ruby@v1
+      with:
+        ruby-version: '3.1.0'
+    - run: ruby $GITHUB_ACTION_PATH/main.rb
+      shell: sh
+      env:
+        API_TOKEN: ${{ inputs.apiToken }}
+        ROOM_ID: ${{ inputs.roomId }}
+        TITLE: ${{ inputs.title }}
+        MESSAGE: ${{ inputs.message }}
diff --git a/entrypoint.sh b/entrypoint.sh
deleted file mode 100755
index 31fde5d..0000000
--- a/entrypoint.sh
+++ /dev/null
@@ -1,8 +0,0 @@
-#!/bin/bash -l
-
-# Chatwork APIを用いてメッセージを投稿する。
-# $1: APIキー
-# $2: ルームID
-# $3: タイトル
-# $4: メッセージ
-ruby send_message.rb $1 $2 "$3" "$4"
diff --git a/send_message.rb b/main.rb
similarity index 81%
rename from send_message.rb
rename to main.rb
index d876d88..d88885d 100644
--- a/send_message.rb
+++ b/main.rb
@@ -1,10 +1,10 @@
 require 'net/http'
 
 params = { 
-  token: ARGV[0],
-  room_id: ARGV[1],
-  title: ARGV[2][1, ARGV[2].length - 2],
-  message: ARGV[3][1, ARGV[3].length - 2]
+  token: ENV['API_TOKEN'],
+  room_id: ENV['ROOM_ID'],
+  title: ENV['TITLE'],
+  message: ENV['MESSAGE']
 }
 
 uri = URI.parse("https://api.chatwork.com/v2/rooms/#{params[:room_id]}/messages")