A switching power supply device having: a power supply terminal VCC connected to one end of an output capacitor Co2; a high-voltage terminal VH connected to the input side of an input voltage Vdc; and a starting circuit 101 provided between the power supply terminal VCC and the high-voltage terminal VF, the starting circuit 101 passing a first current for charging the output capacitor Co2 via the power supply terminal VCC. The switching power supply device is provided with: a control circuit 10 for turning a switching element M1 on and off; and a current-supplementing circuit 30 to which the input voltage Vdc is inputted, the current-supplementing circuit 30 being connected to the high-voltage terminal VH, the current-supplementing circuit 30 passing a second current to the output capacitor side on the basis of the first current. A load L2 can be connected to the other end of the output capacitor.