PURPOSE: To reduce power consumption by disposing a second switch for feeding a constant voltage to a first relay driving section only when a switch is turned ON thus operating the relay driving section at a first control section.

CONSTITUTION: When a switch 500 is turned ON in order to interrupt an alarm produced upon interruption of a secondary power supply, a second switch 600 disposed at a first control section 700 is turned ON. Consequently, a voltage is fed to a first relay driving section 100 thus operating the first relay driving section 100 and the contact 300 of corresponding relay is opened thus interrupting provision of an alarm. On the other hand, upon turning the switch 500 OFF, the second switch 600 disposed at the first control section 700 is turned OFF to interrupt voltage supply to the first relay driving section 100. Since the second switch 600 is turned OFF upon turn OFF of the switch 500 to interrupt current supply to the first control section 700, high current is not consumed at the first control section 700.