PURPOSE: To prevnt the head of speech from being missed by providing a switch decreasing the gain of a transmission/reception circuit to a desired gain and also fixing the attenuation of the transmission/reception circuit to a small value at a short distance talking to bring about the simultaneous transmission/reception state with the operation of the switch.

CONSTITUTION: Trunk lines L1, L2 are connected to a voice amplifier 2 via a hybrid circuit 1, and after a voice signal is amplified at reception, its output is fed to a variable attenuator 15 and a switch control circuit 14. The output of the attenuator 15 is fed to an output amplifier 12 provided with gain adjuster and its output drives a speaker 5. Moreover, an output of microphone 6 is amplified by a voice amplifier 13 provided with gain adjuster, its output is fed to the circuit 4 and the variable attenuator 16, and an output of he attenuator 16 is transmitted to the trunk lines L1, L2 via a voice amplifier 9 and the circuit 1. A talking mode changeover switch 11 is provied between the amplifiers 12 and 13, the gain of the amplifiers 12, 13 is brought into a desired value by controlling the circuit 14 to control switches S1, S2 of the attenuators 15, 16 thereby fixing the attenuation to a prescribed value.