Even when, for example, electric charge is injected into the output transistor due to external factor such as a noise from the outside, to prevent the step-down voltage from rising, the step-down circuit is comprised of an N channel type output transistor which controls the voltage at the control end, a booster, which is connected to the control end of the output transistor and raises the voltage at the control end and a discharge circuit, which discharges the electric charge at the control end of the output transistor so that the power supply voltage inputted from the input end is stepped down to a desired step-down voltage and outputted from the output end.