PURPOSE: To attain the cutting-back operation of a transmission line by remote control by permitting a receiver to receive a multifrequency code and to automatically operate a cutting-back switch when the code is coincident with a previously decided signal frequency.

CONSTITUTION: If a B station detects the failure of an in-use transmission line 201, a transmission line is automatically switched from a transmission line 201 to spare transmission lines 211 to 212. Then, this controller is provided with a controller 50 cutting-back from the transmission line 211 and 212 to the transmission line 201 when the transmission line switching switch 102 of the station B is cutting-back-operated. A station C different from the station B is provided with a transmitter 70 generating the multifrequency code obtained by combinating plural frequency signals in accordance with the switch 102 of the station B and transmitting it to the station B, which is provided with the receiver 73 receiving/decoding the multifrequency code from the transmitter 70 and cutting-back-operating the switch 102 of the station. The information line 72 (a telephone line, for example) connects the transmitter 70 and the receiver 73. Thus. the cutting-back of the transmission line can be operated by remote control.