To obtain the small capacity of a preliminary power source by operating a security device in a long time by the preliminary power source to be used at the time of the interruption of an alternating power source.

Receiving circuits M3-M6 are connected with security equipment 3-6, and the receiving circuit M3 is directly connected with a controller CPU, and the receiving circuits M4-M6 are connected through power supplying and interrupting circuits 15 with the controller CPU. A commercial power source 10 is DC converted and supplied from a power source circuit 11 to the controller CPU. When the power interruption of the commercial power source 10 is detected by a power supply and interruption detecting circuit 12, it is switched to a preliminary power source 13 by a changeover switch 14, and power is supplied. In this case, the power is not supplied to the receiving circuits M4-M6 by the power supplying and interrupting circuits 15, and the power is supplied only to the receiving circuit M3 so that a security equipment connected with the receiving ciruit M3 can be operated. When a received signal 82 is outputted from the receiving circuit M3, an alarming sound is generated from a speaker Sp, display lamps LED1 and LED2 are turned on, and the generation of an emergency situation is reported.