In an in-vehicle device remote control system, a vehicle-side device determines in which detection area an electronic key exists based on a response signal transmitted from the key in response to request signals, and a control door to be operated in correspondence to the detection area in which the key exists. The vehicle-side device notifies a user that the key is an authorized one by light, sound, display or the like on the determined control door. With this operation, it is readily recognized by the user because the user is approaching the control door.