PURPOSE: To ensure the service, by making the test operation of a transmitter possible without giving the interference to the external when no voice calls exist in the transmitting device which discriminates the voice in an input signal to control the transmission of the output signal.

CONSTITUTION: When a traffic of call exists, a detector 20 detects always that the voice exists in the input signal, and an input switch 16 and an output switch 18 are closed, and the output signal from the transmitter is transmitted to an antenna 10 to continue the call. When the voice does not exist in the input signal, a controller 19 opens the output switch 18 immediately, and the switch 16 is left closed by the clock signal of a clock signal generator 22, and thus, a current transmitter 5a and a stand-by transmitter 5b can start the test operation by the input signal including no voice.