A power supply apparatus includes a switching regulator, a linear regulator, a timer circuit, a control circuit, an inverter, and a switch. The power supply apparatus is a step-down type DC-DC converter which steps down an input voltage inputted to an input terminal and then outputs an output voltage, which has been stepped down, to an output terminal. The timer circuit counts the time elapsed from when a start of the power supply apparatus is instructed by a control signal, and sets an output signal to a high level at a lapse of a predetermined time. When the output signal goes to the high level, the switch turns on and the output voltage is supplied to a power supply terminal of the control circuit.