PURPOSE: To make it possible to speedily recover a fault by immediately informing an alarm to an operator by pocket bell in case a variation in the state of the monitor information of a slave station is detected while the operator of the master station is absent.

CONSTITUTION: The absence switch 14 in the master station 1 is turned to B-side when the operator is present at the master station, and a state-variation detecting part 12 is connected to an alarm tone output part 15. When departing the master station, the operator turns the switch 14 to A-side, and the part 12 is connected to an alarm telephone part 13 and the output part 15. A slave station 2 transmits monitor information (a) from its monitor information transmission part 21 to the master station 1 through a dedicated line 3. On the master station 1-side, the information is received by a monitor information receiving part 11, and a state-variation is detected by the detecting part 12. When a state-variation is detected by the part 12 while the operator is absent, a special dial signal is transmitted from the telephone part 13 to a radio call network 4. From a base station 41 in the network 4, a pocket bell electromagnetic wave (b) is transmitted to ring a pocket bell 5.