PURPOSE: To attain simultaneous talking by applying a specific DC voltage to a semiconductor negative element to constitute a 2-way amplifier.

CONSTITUTION: In talking from the position P to the position Q a sound current generated by a microphone M1 is amplified by a semiconductor two-way amplifier A1, transmitted to the Q position, a part of the signal enters an amplifier A2 to actuate a speaker S2. The DC current of the amplifier A2 is transmitted from the P to the Q through transmission lines L, L' together with the sound current. In the talking from the Q to the P, the sound current generated by a microphone M2 is given to the 2-way amplifier A1 through a capacitor C3 and the transmission lines L, L', a part is fed to the amplifier A3 to actuate a speaker S1.