A switching power source apparatus has a switching element Q1. Between terminals of the switching element Q1, there is parasitic capacitance (C1, C2). A voltage V4 of parasitic oscillation appears at a gate of the switching element Q1 after a flyback period. A voltage detector detects a drop in the voltage V4 and outputs a detection signal V6. The detection signal V6 is delayed by a timer, which outputs an ON start signal synchronized with timing T at which the voltage V4 reaches a bottom level. In response to the ON start signal from the timer, a controller outputs an ON control signal to turn on the switching element Q1. In response to the ON control signal from the controller, a driver applies a drive signal to the gate of the switching element Q1, thereby driving the switching element Q1.