A switching power supply apparatus includes first and second switch circuits (S1) and (S2) including switch devices (Q1) and (Q2), diodes (D1) and (D2), and capacitors (Cds1) and (Cds2), and a transformer (T). A first inductor (Lr) is connected in series with a primary winding (Lp) of the transformer (T), and a second inductor (Li) is arranged so that a voltage of a third capacitor (Ca) is applied during an on-period of the first switch circuit (S1). A diode (Di) preventing a reverse current from flowing in the second inductor (Li), and a capacitor (Ci) that is charged by excitation energy stored in the second inductor (Li) and that applies a voltage to the primary winding (Lp) during the on-period of the first switch circuit (S1) are further provided. A capacitor (Cr) is further provided so as to define a closed loop together with the inductor (Lr), the primary winding (Lp), and the second switch circuit (S2).