NOVELTY - The device (50) has rectifying unit (10) to rectify alternating current, and control unit (51). A step-up/step-down unit (20) includes MOSFET (23) for improving power factor and stepping up or stepping down direct current voltage from rectifying unit. A capacitor (15) is charged by direct current voltage and is discharged toward output unit (39) at later stage. Early-stage switching elements (11,12) are arranged in series between step-up/step-down unit and capacitor, and later-stage switching elements (16,17) are arranged in series between capacitor and output unit.    USE - Power conversion device for charging batteries used in electric vehicle and plug-in type hybrid vehicle.    ADVANTAGE - The loss in the power conversion device can be reduced, while enabling change in the input and output voltage at wider range. The reactive power can be decreased by shaping input electric current waveform from alternating current power supply using switching elements, inductors and capacitors. The rush current can be prevented by making gate voltage of switching elements into zero when the voltage becomes more than the reference voltage, hence failure of the power supply device is prevented. The security of the power conversion device is improved, as the switching element of OFF state interposes between alternating current input side and output side when transmitting the electric charge to the output unit. The load to the domestic power distribution system can be reduced by improving power factor by the switching element. The electric power can be exchanged mutually, as the switching element can be made into bi-directional with reverse-blocking capability. The cost of the power conversion device is reduced by combining insulated gate bipolar transistor without reverse blocking capability and normal diode.    DESCRIPTION OF DRAWING(S) - The drawing shows a circuit block diagram of power conversion device.(Drawing includes non-English language text)    Rectifying unit (10)    Early-stage switching elements (11,12)    Central capacitor (15)    Later-stage switching elements (16,17)    Step-up/step-down unit (20)    MOSFET (23)    Output unit (39)    Power conversion device (50)    Control unit (51)