NOVELTY - The device (1) includes two electric power lines (11), voltage increasing unit (2), smoothing capacitor (3) and diode (5) for discharge prevention. A switch (4) is electrically connected between one terminal (210) of power supply (12) and one terminal (30) of smoothing capacitor. The switch is OFF when supplying electric power to direct current (DC) load (10) from power supply. The electric charge stored in smoothing capacitor is discharged through switch and first reactor (21) of voltage increasing unit by turning ON switch after stopping electric power supply from power supply to DC load.    USE - Power supply device used for vehicle-mounted power converter device or inverter and charging device. Can be used for charging device used in charging the battery mounted in e.g. hybrid vehicle, electric vehicle.    ADVANTAGE - Provides a power supply device with smoothing capacitor discharging function, in which the electric charge stored in the smoothing capacitor is discharged using a discharge current that attenuates the resistance component of the first reactor. Prevents electric shock accidents by discharging the smoothing capacitor. Ensures reduced manufacturing cost of the power supply device due to reduced size of the power supply device and omission of a separate reactor for discharge. Ensures efficient discharge of smoothing capacitor while ensuring reduced size of the power supply device.    DETAILED DESCRIPTION - The terminals (30,31) of the smoothing capacitor are respectively connected to the electric power lines at the positive and negative sides (11p,11n). The first reactor is connected to the other terminal (31) of the smoothing capacitor. The smoothing capacitor may be provided in the form of an electrolytic capacitor, while the switch is provided in the form of a semiconductor switch.    DESCRIPTION OF DRAWING(S) - The drawing shows the circuit diagram of the power supply device.    Power supply device (1)    Voltage increasing unit (2)    Smoothing capacitor (3)    Diode (5)    DC load (10)    Electric power lines (11)    Electric power lines at the positive and negative sides (11p,11n)    Power supply (12)    First reactor (21)    Terminals of smoothing capacitor (30,31)    Terminal of power supply (210)