NOVELTY - The power supply device has a battery unit (1) having several batteries (10) which are connected in series. An earth-leakage detection circuit (5) is provided to detect the earth-leakage of the battery unit. An electric power supply is provided to the load (30) connected to the output side of the battery unit through a direct current (DC)/alternating current (AC) converting circuit (31). The earth-leakage detection circuit is provided to detect the variation of the voltage, and to detect the earth-leakage of the output side of the DC/AC converting circuit.    USE - Power supply device mounted in vehicle such as plug-in type hybrid electric vehicle and electric vehicle, and for use in electrical storage apparatus (all claimed) such as backup power supply apparatus for wireless base station, rack of computer server, mobile telephone, home internal, power supply for electrical storage for factory, power supply of street light, and signal apparatus.    ADVANTAGE - The earth-leakage detection circuit is provided to detect the variation of the voltage, and to detect the earth-leakage of the output side of the DC/AC converting circuit, thus the AC component of detection voltage can be detected, and the earth-leakage of load can be detected. The input side of load is connected to the output side of battery unit through the small resistance, and the AC component can be increased, when the electrical resistance of earth leakage resistance can be reduced, thus the magnitude of earth-leakage resistance can be detected based on the level of the AC component. The circuit structure of the power supply device can be simplified.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for the following:    (1) a vehicle; and    (2) an electrical storage apparatus.    DESCRIPTION OF DRAWING(S) - The drawing shows a circuit diagram of the power supply device. (Drawing includes non-English language text)    Battery unit (1)    Earth-leakage detection circuit (5)    Battery (10)    Load (30)    DC/AC converting circuit (31)