To provide an extended controller which improves the operability of a video game to be played with a mobile telephone set, thereby enabling a player to enjoy a game as if the player is using a home video game machine.

The controller is provided with a machine body holding mechanism combined with the mobile telephone set to hold this, hand held structures 14 and 16 projecting to both sides of the mobile telephone set and to be supported by both hands of the user in a combined state, a plurality of operation elements 22 arranged on the front surface of these structures 14 and 16 and to be operated with the finger tip of a user, a signal generation means incorporated into the structures 14 and 16 to generate an electrical signal corresponding to the change of the element 22, and a signal transmission means for transmitting the output signal of this signal generation means to the data terminal of the mobile telephone set.