To prevent the malfunction of a DC load by suppressing the difference in the voltage supplying time to the load by providing an AC voltage monitoring circuit which sends turning-on signals to all switching elements, after confirming that an AC voltage is normally impressed upon all switching elements to a power source circuit which receives AC power from multiple systems and has the switching elements at every system.

When circuit breakers 21-2n are turned on, an AC voltage monitoring circuit 5 confirms the state of each AC voltage at a cabinet panel 1 which receives AC power from multiple systems and, after confirming that the states are normal, turns on relays 31-3n. Consequently, the AC voltages of the systems are impressed upon power source modules 41-4n and all DC voltages are impressed at once upon a DC load 7. When the voltage supply is turned off by means of the circuit breakers 21-2n, the relays 31-3n are turned off by means of the output of the monitoring circuit 5, with the turning off being triggered by the turning off of an arbitrary one system, and the impression of the AC voltage upon the modules 41-4n is stopped. Therefore, the occurrence of a fault, such as the latch up, etc., in the DC load 7 can be prevented.