A communication system that permits the coexistence of a plurality of ultrawide band (UWB) radio communication networks that use different signal systems is achieved by using the same beacon signal and specifying the format of part of the control command among a plurality of UWB radio communication networks that use different signal systems, as defined, for example, by impulse period, impulse width, spreading ratio, and spreading code. When one UWB network receives a beacon signal from another UWB network, judging from the received beacon signal it grasps the transmission parameter that is used by another party and performs time-division on the transmission frame period for its own system.