PURPOSE: To attain smooth talking by detecting a reception state of a reception signal to inhibit the transmission of the signal during reception thereby avoiding crosstalk.

CONSTITUTION: In the case of the reception mode in which a signal is sent from a base station or the like through a radio channel to an antenna 5, the received signal is demodulated by a reception section 6 via a changeover device 4, amplified by a low frequency amplifier 7 and outputted from a speaker 8. Then a detection interrupt control circuit 9 detects an output signal from the low frequency amplifier 7 and when its output signal is a prescribed level or over, an interrupt control signal is outputted to a transmission section 3. Upon the receipt of the interrupt control signal, the transmission section 3 interrupts the signal transmission and stops the transmission even when the signal to be sent is received from a microphone 1 and a modulation section 2. Thus, even when a received voice signal or an external noise is bypassed to the microphone 1 causing the same state that the user speaks to the microphone 1 during the reception mode, the transmission mode is not selected and crosstalk is prevented.