PURPOSE: To eliminate the over discharge of a battery and to prevent the breakdown of software by providing an apparatus with a relay to be reset at the time of insufficient capacity of a power failure backup battery and with a means notifying a computer of a power failure.

CONSTITUTION: In an apparatus switching from a through circuit 15 to an inverter 14 getting electricity from a backup battery 5 by a switching means 16 to supply power at the time of power failure of a commercial power supply, a latching relay 6 to be reset at the time of insufficient capacity of the battery 5 is inserted into a feeder path on the battery 5 side. Also, there is provided a microprocessor 20 for transmitting a power failure notification to a computer via RS232C interface 22 and receiving a notification of completion of emergency refuge from said computer. In this manner, the over discharge of the battery 5 is eliminated and the breakdown of computer software can be prevented.