--- a/config/environments/development.rb	Mon Jun 13 15:07:38 2016 +0900
+++ b/config/environments/development.rb	Sat Jul 02 17:04:25 2016 +0900
@@ -42,6 +42,9 @@
   # Raises error for missing translations.
   config.action_view.raise_on_missing_translations = true
 
+  # Suppress logger output for asset requests.
+  config.assets.quiet = true
+
   # Use an evented file watcher to asynchronously detect changes in source code
   # routes, locales, etc. This feature depends on the listen gem.
   # config.file_watcher = ActiveSupport::EventedFileUpdateChecker