A communication system includes a main communication unit, a subcommunication unit that communicates with the main communication unit by using first wireless channels, and an external communication unit that communicates with the main communication unit by using second wireless channels. The subcommunication unit includes a state detection unit that detects a use state of the second wireless channels. The main communication unit includes a state acquisition unit that acquires the use state of the second wireless channels, a selection unit that selects a predetermined number of the first wireless channels with the less effect of radio wave interaction in the wireless communications based on the use state, a channel determination unit that determines one of the predetermined number of the first wireless channels, and a first wireless communication unit that communicates with the subcommunication unit using the one of the predetermined number of the first wireless channels.