To provide an attachment for a controller capable of responding to a plurality of existing controllers of a home video game machine.

The attachment 1 of the controller for the game machine is removably mounted to various controllers 15 for the game machine where a plurality of keys 151-155 have a common key 151 so that the attachment 1 responds to the common key 151. Movable parts 12 and 13 corresponding to the plurality of keys 151-155 are removably disposed in the attachment 1.