A multiple-output switching power supply unit includes: a voltage generating circuit Q1, Q2, T1a, 10a configured to generate a pulse voltage by intermittently interrupting a direct current power supply 1; a series resonance circuit including a current resonance capacitor Cri2, a primary winding P2 of a transformer T2, and a switching element Q3, the pulse voltage generated in the voltage generating circuit being applied to the series resonance circuit; a rectifying/smoothing circuit D2, C2 configured to rectify and smooth a voltage which is generated in a secondary winding S2 of the transformer, and thus to output a direct current output voltage; and a control circuit 11 configured to turn on and off the switching element based on the direct current output voltage.