diff --git a/doc/irb/irb.rd.ja b/doc/irb/irb.rd.ja
index 6f55b0176..633c08cbd 100644
--- a/doc/irb/irb.rd.ja
+++ b/doc/irb/irb.rd.ja
@@ -51,6 +51,12 @@ irbの使い方は, Rubyさえ知っていればいたって簡単です. 基本
 		    オブジェクトの作成方法を 0 から 3 のいずれかに設定する.
   --echo	    実行結果を表示する(デフォルト).
   --noecho	    実行結果を表示しない.
+  --echo-on-assignment
+                    代入時に実行結果を表示する.
+  --noecho-on-assignment
+                    代入時に実行結果を表示しない.
+  --truncate-echo-on-assignment
+                    代入時に省略された実行結果を表示する(デフォルト).
   --inspect	    結果出力にinspectを用いる.
   --noinspect	    結果出力にinspectを用いない.
   --singleline      シングルラインエディタを利用する.
diff --git a/lib/irb.rb b/lib/irb.rb
index 0cad6a0d4..fad738f7c 100644
--- a/lib/irb.rb
+++ b/lib/irb.rb
@@ -64,6 +64,12 @@
 #                       when new workspace was created
 #     --echo            Show result (default)
 #     --noecho          Don't show result
+#     --echo-on-assignment
+#                       Show result on assignment
+#     --noecho-on-assignment
+#                       Don't show result on assignment
+#     --truncate-echo-on-assignment
+#                       Show truncated result on assignment (default)
 #     --inspect         Use `inspect' for output
 #     --noinspect       Don't use inspect for output
 #     --multiline       Use multiline editor module
diff --git a/lib/irb/context.rb b/lib/irb/context.rb
index 6dc5d7f0f..09fd840bd 100644
--- a/lib/irb/context.rb
+++ b/lib/irb/context.rb
@@ -274,6 +274,18 @@ def main
     #     IRB.CurrentContext.echo_on_assignment = true
     #     a = "omg" * 10
     #     #=> omgomgomgomgomgomgomgomgomgomg
+    #
+    # To set the behaviour of showing on assignment in irb:
+    #
+    #     IRB.conf[:ECHO_ON_ASSIGNMENT] = :truncate or true or false
+    #
+    # or
+    #
+    #     irb_context.echo_on_assignment = :truncate or true or false
+    #
+    # or
+    #
+    #     IRB.CurrentContext.echo_on_assignment = :truncate or true or false
     attr_accessor :echo_on_assignment
     # Whether a newline is put before multiline output.
     #
diff --git a/lib/irb/lc/help-message b/lib/irb/lc/help-message
index fe9e3246d..cee860fde 100644
--- a/lib/irb/lc/help-message
+++ b/lib/irb/lc/help-message
@@ -22,6 +22,12 @@ Usage:  irb.rb [options] [programfile] [arguments]
                     when new workspace was created
   --echo            Show result (default)
   --noecho          Don't show result
+  --echo-on-assignment
+                    Show result on assignment
+  --noecho-on-assignment
+                    Don't show result on assignment
+  --truncate-echo-on-assignment
+                    Show truncated result on assignment (default)
   --inspect         Use `inspect' for output
   --noinspect       Don't use inspect for output
   --multiline       Use multiline editor module
diff --git a/man/irb.1 b/man/irb.1
index 113b986b1..a8a9b60a5 100644
--- a/man/irb.1
+++ b/man/irb.1
@@ -112,6 +112,16 @@ Show result (default).
 Don't show result.
 .Pp
 .Pp
+.It Fl -echo-on-assignment
+Show result on assignment.
+.Pp
+.It Fl -noecho-on-assignment
+Don't show result on assignment.
+.Pp
+.It Fl -truncate-echo-on-assignment
+Show truncated result on assignment (default).
+.Pp
+.Pp
 .It Fl -colorize
 Use colorization.
 .Pp