A switching power supply circuit includes a converter transformer in which an output obtained by switching a direct current voltage of a converter through resonance is transmitted from the primary side to the secondary side. The switching power supply circuit further includes, on the secondary side of the converter transformer, a secondary step-up winding wound on a portion of a core together with a primary winding, and a low voltage secondary winding wound on another portion of the core. On the secondary side of the converter transformer, an alternating voltage obtained from the step-up winding is utilized to produce a direct current high voltage, and an alternating voltage obtained from the low voltage secondary winding is utilized to produce a direct current low voltage. Consequently, two different direct current outputs including the direct current high voltage and the direct current low voltage are obtained from the converter transformer.