PURPOSE: To make a voice channel alone enough for a transmission line, and besides, to improve a transmitting efficiency because it is not necessary to reduce the number of the bits of a voice signal by transmitting a control signal as well through the use of the transmission line of a voice information.

CONSTITUTION: A transmission controlling pulse (d) is supplied to AND circuits 6, 7, and when the pulse (d) is 1-level, the output Q of a register 2 is transmitted, and when it is 0-level, the voice information, supplied to a voice information input terminal 8, is transmitted. This signal is transmitted from an OR circuit 9 and an output terminal 10. At a receiving side, it is supplied to and input terminal 20, and is supervised by shift registers 21∼23, an EOR 24, delay switching circuits 25, 26 and the AND circuit 27, etc., and a reception controlling pulse is outputted from the delay switching circuit 26. The said reception controlling pulse is supplied to the register 28 through the AND circuit 30, and the reception controlling pulse is outputted. The said signal energizes a relay 31, and makes a contact 31a into ON, and the control signal is outputted from the output terminal 32. In such a way, the control signal can be transmitted by using the voice channel.