PURPOSE: To shorten fault detecting period of a repeating station and a slave station in a time-divided multiplex communication system.

CONSTITUTION: A call processing control circuit 90 executes originating/ terminating call control processing, a talking station detecting circuit 100 detects a repeating station and a slave station in talking, a control signal switching circuit 110 outputs a switching signal for using a call processing control signal transmitting use time slot for a station monitoring signal by switching it from use of a call processing signal which is not required in talking as use of a station monitoring signal based upon an output signal from the circuit 100. The 1st selector circuit 10 selects a station monitoring signal outputted from a station monitor and control circuit 80 and the station monitoring signal is time-divided and multiplexed with the call processing control signal transmitting use time slot. On the receiving side, the signal of a call processing control signal transmitting use time slot signal separated by a control signal separating circuit 60 is a response signal to a monitor signal and is outputted to the 2nd selector circuit 70 and then outputted to the circuit 80.