PURPOSE: To improve howling margin of a speech circuit and the tracking with respect to a change in the talking state by providing a loss circuit whose attenuation rate is changed independently to a conventional speech circuit in addition to two loss circuits for howling prevention.

CONSTITUTION: A large variation of an attenuation rate of a variable loss circuit 6 attenuating a transmission signal is desired between the transmission mode and the reception mode in order to avoid howling in the transmission mode and the reception mode surely. Then the variation of the attenuation rate in a change-over variable loss circuit 18 between the transmission mode and the reception mode is selected small and that of variable loss circuits 6, 9 is selected large. Then howling is surely avoided and an output signal of a comparator circuit 14 changes quickly in following to the change between the transmission mode and the reception mode or vice versa. Thus, the howling margin is increased but the tracking performance of the speech circuit with respect to the change in the talking state is not lost.