A control system includes a portable device transmitting to a proximity control signal controlling locking/unlocking of an opening/closing body of the vehicle from near the vehicle, and a remote control signal controlling an engine remotely, intensity of the remote control signal higher than the proximity control signal, and a control device receiving a signal transmitted by the portable device. The portable device transmits by a same transmission antenna the whole of the proximity control signal at a single center frequency, and all of divided signals obtained by dividing the whole of the remote control signal into plural pieces at plural center frequencies. The control device receives by a same reception antenna the whole of the proximity control signal at the single center frequency, and all of the divided signals at center frequencies corresponding to frequencies used upon transmission of the divided signals by the portable device.