A first primary winding N11 of a transformer 1 is connected with a commercial power source 30 via a transistor Q1, and a second primary winding N22 of the transformer 1 is connected with a backup battery 31 via a transistor Q2. An electric power on the second primary winding N12 is output for a controlling apparatus. When a voltage of the commercial power source 30 is larger than a predetermined value, a backup stopping circuit 10 turns off a LED 9 and stops the transistor Q2. The second primary winding N22 is connected with input terminals 14, 15 as a power source for charging a battery 31. While the transistor Q2 is stopped, an electric power for the battery is output from the second primary winding N22. Since the LED 9 turns on at the time of electric power breakdown, the electric power for the battery is stopped.