PURPOSE: To identify the end of communication due to the passage of a communication enabled time by a receiving station by transmitting a signal for noticing the end of the communication-enabled time from a transmitting station.
CONSTITUTION: When the transmitting station starts communication with the receiving station, a system control part 136 excites a timer circuit 130 to count up communication passage time. When the counted value approaches the end of the communication-enabled time, the control part 136 controls a procedure control part 128 and transmits an alarm signal from a transmission/reception circuit 200 through a procedure signal sending part 112. In the receiving station, the alarm signal included in the signal received by a transmission/reception circuit is recognized by an alarm signal detecting circuit 156. When the alarm signal is detected, prescribed communication end processing is executed. Thus, the end of communication due to the passage of the communication-enabled time can be identified by the receiving station.