diff --git a/io.c b/io.c
index 2a5a645..91178a6 100644
--- a/io.c
+++ b/io.c
@@ -7339,11 +7339,51 @@ select_end(VALUE arg)
  *     IO.select(read_array
  *               [, write_array
  *               [, error_array
- *               [, timeout]]] )-> array  or  nil
+ *               [, timeout]]]) -> array  or  nil
  *
- *  See <code>Kernel#select</code>.
+ *  Calls select(2) system call.
+ *  It monitors given arrays of <code>IO</code> objects, waits one or more
+ *  of <code>IO</code> objects ready for reading, are ready for writing,
+ *  and have pending exceptions respectably, and returns an array that
+ *  contains arrays of those IO objects.  It will return <code>nil</code>
+ *  if optional <i>timeout</i> value is given and no <code>IO</code> object
+ *  is ready in <i>timeout</i> seconds.
+ *
+ *  === Parameters
+ *  read_array:: an array of <code>IO</code> objects that wait until ready for read
+ *  write_array:: an array of <code>IO</code> objects that wait until ready for write
+ *  error_array:: an array of <code>IO</code> objects that wait for exceptions
+ *  timeout:: a numeric value in second
+ *
+ *  === Example
+ *
+ *      rp, wp = IO.pipe
+ *      mesg = "ping "
+ *      100.times {
+ *        rs, ws, = IO.select([rp], [wp])
+ *        if r = rs[0]
+ *          ret = r.read(5)
+ *          print ret
+ *          case ret
+ *          when /ping/
+ *            mesg = "pong\n"
+ *          when /pong/
+ *            mesg = "ping "
+ *          end
+ *        end
+ *        if w = ws[0]
+ *          w.write(mesg)
+ *        end
+ *      }
+ *
+ *  <em>produces:</em>
+ *
+ *      ping pong
+ *      ping pong
+ *      ping pong
+ *      (snipped)
+ *      ping
  */
-
 static VALUE
 rb_f_select(int argc, VALUE *argv, VALUE obj)
 {