diff --git a/doc/source/reference/functions/in_values.rst b/doc/source/reference/functions/in_values.rst
index ab6a08c553..90d8bd6562 100644
--- a/doc/source/reference/functions/in_values.rst
+++ b/doc/source/reference/functions/in_values.rst
@@ -11,12 +11,18 @@ in_values
 Summary
 -------
 
-TODO
+``in_values`` function is added since Groonga 4.0.7.
+
+``in_values`` enables you to simplify the query which uses multiple ``OR`` or ``==``. It is recommended to use this function in point of view about performance improvements in such a case.
 
 Syntax
 ------
 
-TODO
+``query`` requires two or more arguments - ``target_value`` and multiple ``value``.
+
+::
+
+  in_values(target_value, value1, ..., valueN)
 
 Usage
 -----