A switching power supply apparatus includes a PFC converter, a DC-DC converter, and primary-side and secondary-side digital control circuits that control the PFC converter and the DC-DC converter. On the basis of a voltage detected by an output voltage detection circuit, the primary-side digital control circuit transmits data about the on-time of a switching element of the DC-DC converter to the primary-side digital control circuit. On the basis of this data, the primary-side digital control circuit controls the on-time of the switching element.