PURPOSE: To attain full duplex communication in different direction by means of a general purpose 4-wire type exchange by using an out going-only channel and an incoming-only channel in the case of facsimile communication and using the outgoing-only channel at an outgoing side and the outgoing-only channel at the incoming side in thecase of the telephone communication.

CONSTITUTION: The 4-wire type exchange 1 is a general purpose exchange and provided with line interface sections 6-1∼6-n comprising respectively an outgoing side reception interface 2 corresponding to the outgoing-only channel, the outgoing transmission interface 3, the incoming reception interface 4 corresponding to the incoming-only channel and the incoming side transmission interface 5. Full duplex exclusive units 7-1∼7-n are connected respectively, the outgoing reception interface 2 is connected to the input of the amplifier 9 via a low pass filter 8, the transmission interface 3 at the outgoing side is connected to the output side of an amplifier 10, the incoming reception interface 4 is connected to the input of the amplifier 9 via a high pass filter 11 and the transmission interface 5 at the incoming side is connected to the output side of the amplifier 10 via a low pass filter 12.