To provide a switching power supply that has high efficiency even in a light load state despite a large output, low noise two-element half bridge resonant type.

A switching power supply 80 has a switch section for switching a resonance point of an LC resonance circuit. In accordance with the status of a load, the resonance point and an operating frequency are switched to appropriate ones. This can improve efficiency in a light load state, so that the switching power supply 80 operates with high efficiency in both heavy and light load states.