To provide miniaturization and cost reduction for a circuit by suppressing the generation of inrush current without using a charging resistor.

A charging voltage detector 11 turns off a low-speed switch 8, and monitors a potential difference across the low speed switch 8. If the potential difference is equal to or above a prescribed value, it determines that the charging of a smoothing capacitor 7 has not completed, and produces and outputs switching pulses for on-driving a high-speed switching element 6. If the potential difference is less than the prescribed value, it determines that the charging of the smoothing capacitor 7 has completed and turns on the low-speed switch 8. It is thus possible to suppress generation of inrush current by attaching a charging diode 4 alone without using a charging resistor.