To reduce an inrush current to a switched capacitor and an output smoothing capacitor when power is applied to a charge pump circuit.

A DC/DC converter (2) converts a DC voltage from a DC power supply (1) by slow start where a voltage output is increased to a desired voltage level over a predetermined time. The charge pump circuit (3) boosts an output voltage from the DC/DC converter (2) so that the voltage level is doubled. The charge pump circuit (3) consists of MOS transistors (Q1-Q4), a switched capacitor (C1), and an output smoothing capacitor (C2). A drive circuit (4) controls switching of the MOS transistors (Q1-Q4) by a drive signal having a voltage level which increases gradually after starting operation of the charge pump circuit (3).