According to one embodiment, a DC-DC converter 1 includes a power supply unit 12 that includes an inductor L1 and a switching unit and generates an output voltage Vout corresponding to a duty of a pulse signal P1, a PID controller 111 that outputs a control signal S corresponding to a difference between a divided voltage of Vout and a target voltage Vcnst, a PI controller 112 that outputs a control signal D corresponding to a difference between the control signal S and an average current flowing through the inductor L1, a PWM generation unit 113 that generates the pulse signal P1 with a duty ratio corresponding to the control signal D, and in step-down mode, the PI controller 112 performs proportional control of the differential signal ei by using a product of the control signal D and a reference proportionality constant KP as a proportionality constant.