diff --git a/ChangeLog b/ChangeLog
index 9a4f946400..17aaf6c5e5 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+Fri Dec 25 21:33:06 2015  Yukihiro Matsumoto  <matz@ruby-lang.org>
+
+	* version.h (RUBY_VERSION): 2.4.0 development has started.
+
 Fri Dec 25 14:12:12 2015  Martin Duerst  <duerst@it.aoyama.ac.jp>
 
 	* doc/ChangeLog-2.3.0, ext/tk/lib/tkextlib/SUPPORT_STATUS,
diff --git a/include/ruby/version.h b/include/ruby/version.h
index 23a9765e91..8b4801fcfd 100644
--- a/include/ruby/version.h
+++ b/include/ruby/version.h
@@ -31,7 +31,7 @@
 
 /* API version */
 #define RUBY_API_VERSION_MAJOR 2
-#define RUBY_API_VERSION_MINOR 3
+#define RUBY_API_VERSION_MINOR 4
 #define RUBY_API_VERSION_TEENY 0
 #define RUBY_API_VERSION_CODE (RUBY_API_VERSION_MAJOR*10000+RUBY_API_VERSION_MINOR*100+RUBY_API_VERSION_TEENY)
 
diff --git a/version.h b/version.h
index c6415d58e0..3d385b1f4f 100644
--- a/version.h
+++ b/version.h
@@ -1,4 +1,4 @@
-#define RUBY_VERSION "2.3.0"
+#define RUBY_VERSION "2.4.0"
 #define RUBY_RELEASE_DATE "2015-12-25"
 #define RUBY_PATCHLEVEL -1