PURPOSE: To form automatically an independent order-wire line, by controlling the termination and connection conditions with an answer signal in a calling mode and with a call signal, a call sound in a called mode respectively.

CONSTITUTION: When a talk switch S1 is applied at the calling side, a call signal is delivered from an oscillating circuit 14 and transmitted to channels 9 and 10 together with a call sound signal of a telephone transmission/reception circuit 13. When the answer signal of a called station is delivered from the side of the channel 10, this signal is supplied to a detecting circuit 16 via a channel branching circuit 29. The detection signal is supplied to an AND circuit 22 via an OR circuit 20 to drive a channel termination control circuit 11 and to terminate the channel 9. In the same way, the switch S1 is applied at a called station. Thus a signal is applied via an AND circuit 21 to drive a channel termination control circuit 12 to terminate the channel 10. In such a way, an independent order-wire line is formed automatically between both stations.