A rectifier circuit for converting an AC voltage to a DC voltage has a first MOS transistor having a source connected to a first input terminal of an AC power supply, and also having a drain connected to an output terminal thereof, a first parasitic diode formed between the first input terminal and the output terminal, a first detection circuit, connected to the first input terminal and to the output terminal, for detecting a difference in voltage between the first input terminal and to the output terminal, a second MOS transistor, adapted to be reverse in polarity to the first MOS transistor, having a source connected to a second input terminal of the AC power supply and also having a drain connected to a ground terminal, a second parasitic diode formed between the input terminal and the ground terminal, a second detection circuit, connected to the second input terminal and the ground terminal, for detecting a difference in voltage between the second input terminal and the ground terminal, and a capacitor connected to the output terminal and the ground terminal. The first detection circuit turns on/off the first MOS transistor according to the difference in voltage, which is detected by the first detection circuit. The second detection circuit turns on/off the second MOS transistor according to the difference in voltage, which is detected by the second detection circuit.