diff --git a/README.md b/README.md
index 97ee9ab..8f15aa9 100644
--- a/README.md
+++ b/README.md
@@ -24,6 +24,10 @@ The default account is username="admin" and password="changeme"
 
 ![fluentd-ui](./docs/screenshots/fluentd-ui.gif)
 
+## Dependency
+
+- ruby 2.1.3 or later (since v0.4.0)
+
 ## To Ubuntu 14.04 user (installed ruby by apt-get)
 
 You also need to install these packages: