In a game system 1 of the present invention, an image capturing device 2 captures a controller 20. The controller 20 includes a plurality of LEDs which express controller numbers assigned to the controller 20 in a game application to be executed, and periodically repeats the turning on and off of an LED in a flashing pattern defined in accordance with the controller number assigned. A cycle of the flashing is set so that the flashing appears to be continuous to a user, on the other hand, so that a continuous turning-off state and a continuous turning-on state are captured alternately in succession by the image capturing device 2. The game device 10 determines if the controller 20 is located in the image capturing space of the mage capturing device 2 based on the captured images which are captured continuously at a predetermined capturing speed by the image capturing device 2.