COMMUNICATION SYSTEM

A communication system includes: a vehicle-mounted device; and a mobile device. The vehicle-mounted device includes: a vehicle side transmission device that transmits a request signal; a vehicle side receiver that receives an operation signal, transmitted from a mobile device side operation unit of the mobile device, and a response signal; and a vehicle side reception control device that controls the vehicle side receiver to receive the operation signal as a first channel signal, and to receive the response signal as a second channel signal. The mobile device includes: the mobile device side operation unit; a mobile device side reception device; and a mobile device side transmission device that transmits the operation signal as the first channel signal, and transmits the response signal as the second channel signal.