A power supply circuit includes a standard voltage generator, a regulator, a capacitor and a discharging circuit. The standard voltage generator is configured to generate a standard voltage. The regulator is configured to control an output voltage by use of a reference voltage based on the standard voltage outputted from the standard voltage generator, and to be capable of being switched ON/OFF. The capacitor is connected in parallel to the regulator between the standard voltage generator and the regulator. The discharging circuit is configured to discharge electrical charges from the capacitor while the regulator is in an OFF state.