PURPOSE: To dispense with a dedicated line switching information transmission part by transmitting line switching information from a supervisory station in a dial signal.

CONSTITUTION: When a satellite line 2 is interrupted, the line switching part 9 of a controller 4 to be monitored receiving a transmitted PB signal returns an incoming tone to a supervisory controller 3 by performing the dial operation of a telephone set 5. A prescribed PB signal is sent out by performing the dial operation of the telephone set 5 at a center side confirming the incoming tone, and also, a supervisory controller 8 is connected to ground switching line 11, 12 sides by switching line switching parts 6, 7 by a manual operation. When a fault is recovered, the transmission line of supervisory control signal is returned to the satellite line 2 by operating the supervisory station, thereby, it is possible to dispense with the dedicated line switching information transmission part.