PURPOSE: To dispense with the periodic transmission of a notification start-up signal by an exchange station and to reduce burden on the exchange station by providing a timer at a base station instead of the exchange station, and transmitting the notification start-up signal periodically.

CONSTITUTION: The exchange station 1 transmits a notification start-up synchronizing signal to the base stations 2a, 2b connected by wire lines 4a, 4b. The base stations 2a, 2b receive the notification start-up signal, and transmit the notification start-up signal at prescribed time intervals t2, and start up their own times. The time interval t2 of the notification start-up signal transmitted from the base stations 2a, 2b is decided by the notification start-up synchronizing signal from the exchange station 1. Also, the base stations 2a, 2b transmit the notification start-up signal at intervals of period t1 successively, respectively, and the period t1 is decided by the timers of the base stations 2a, 2b. The notification start-up synchronizing signal is transmitted from the exchange station 1 at a period t3 sufficiently larger than the period t1 and the time interval t2, and corrects the timers of the base stations 2a, 2b.