By using switching power supplies a, b, and n, which have detection function of over-current, over-voltage and low voltage, in the case where a short-circuit occurred in a load which is connected to output of a switching power supply, and in the case where a MOSFET of the switching power supply is in a short-circuit state and broken, a main power is forced to be off, and a failure log of the switching power supply is stored in a non-volatile memory unit EEPROM; and also in the case where the main power was turned off and on, even if an abnormal log of the switching power supply logged in the non-volatile memory unit, reclosing of the main power is suppressed and which of the switching power supply occurred failure is notified to the outside.