PURPOSE: To attain the use of plural transmission/reception devices within a same area by controlling the reception/transmission with use of a control circuit which secures the blind time to a received signal.

CONSTITUTION: A #3 transmission/reception device is detected by a #1 transmission/reception device as a received signal via a reception antenna 1 and a receiver 2 and validates only the signals received at the look-through time of a controller 3 to perform a transmission operation through a transmitter 4 and a transmission antenna 5. A #2 transmission/reception device receives the transmission signal (A2) of the #1 transmission/reception device that received a target signal A1 and performs a transmission operation (A3). Then the #3 transmission/reception device receives the transmission signal of the #2 transmission/reception device and transmits a signal, (A4). The #1-#3 transmission/reception devices stop the transmission/operations after a fixed time and then performs the reception operations. Thus the sure operations are secured with the transmission/reception devices and at the same time the cost is reduced for these devices.