PURPOSE: To execute switching in a short time at normal switching by executing switching control to an opposite station after the own station is switched and switching back the own station if the switching of the opposite station is not executed.

CONSTITUTION: When a fault is detected in a terminal device, it is received by a trigger reception section 20 of a line switching controller 3 of a station A, a CPU10 extracts a switching instruction in a switching execution program of an ROM11, a latch circuit 14 latches it and transmits the result to a line switching device 1 of the station A and a system SYS1 switches an active line 7-2 into a spare line 7-1. When the switching is finished, the CPU10 recognizes it via a state supervisory section 19 and a buffer 15 to extract the switching command of the opposite station in the switching execution program of the ROM11. The latch 13 latches it, is subjected to parallel/serial conversion at a P/S converter 17 and the switching command is transmitted to the line switching controller 4 of the station B via a transmission section 21 and a supervisory control line 9.