The diode D3 is connected between the node N2 and the capacitor C1 such that a current flows from the node N2 to the capacitor C1.

According to a conventional switching power supply apparatus provided with a bootstrap circuit (for example, see Patent Document 1), two series-connected switching elements operate complementarily. The capacitor of the bootstrap circuit is charged in a time interval in which the high-side switching element is turned off and the low-side switching element is turned on. Therefore, before turning on the high-side switching element, the capacitor of the bootstrap circuit is charged to a sufficiently high voltage to operate the drive circuit of the high-side switching element. In such a conventional switching power supply apparatus, when two switching elements are synchronously turned on and off, the capacitor of the bootstrap circuit cannot be charged when the two switching elements are turned off. Therefore, the voltage of the capacitor of the bootstrap circuit cannot be sufficiently increased before turning on the high-side switching element.