A voltage regulator includes an error amplifier circuit which controls a gate voltage of an output transistor, an overcurrent protection circuit which prevents an overcurrent of the output transistor, and a protection circuit which detects a negative voltage of an output terminal and controls a gate voltage of the output transistor to suppress an overcurrent. The protection circuit includes a MOS transistor which controls the gate voltage of the output transistor, a clamp circuit connected to a gate of the MOS transistor, a semiconductor element having an N-type region connected to the clamp circuit, and a parasitic bipolar transistor constructed from an N-type region connected to the output terminal as an emitter, a P-type substrate as a base, and the N-type region of the semiconductor element as a collector.