In a door control system, in polling collation processing, a start request signal is intermittently transmitted from a vehicle. When a human around the vehicle is detected, a start request signal is transmitted from the vehicle with high output power. A portable device returns a response signal to the vehicle. Furthermore, when the start request signal is transmitted at the high output power, the reception sensitivity is set to be lower than the normal sensitivity. When receiving the response signal from the portable device, the vehicle transmits an ID request signal, and acquires an ID code from the portable device. The ID code thus acquired is collated with each ID code registered in the vehicle. When both ID codes agree, the vehicle doors are unlocked.