An inductor 6 accumulates an energy therein or releases the accumulated energy according to the state of a main switch element 10 being turned ON/OFF. When the inductor 6 releases an energy, if a sub-switch element 12 is in the ON state, a current is passed through a circuit downstream of the sub-switch element 12, thereby increasing an output voltage VO1. The sub-switch element 12 is a P-channel MOS transistor, and a sub-switch control circuit 18 outputs a control signal VCT1 for the sub-switch element 12. A level shift circuit 19 receives an output-side potential VP of the inductor 6, and outputs, as a control signal VG1 applied to the gate of the sub-switch element 12, the potential VP if the control signal VCT1 is at the L level or a potential (VP-VM) lower than the potential VP if the control signal VCT1 is at the H level. Thus, the output voltage of the DC-DC converter can be made precisely equal to the target voltage.