A rectifier 107 includes a rectifying MOSFET 101 that performs synchronous rectification, a control circuit 106 that inputs a voltage across a pair of a positive-side main terminal TK and a negative-side main terminal TA of the rectifying MOSFET 101 to determine an ON or OFF state of the rectifying MOSFET 101 based on the inputted voltage, and a capacitor 104 that supplies power to the control circuit 106. The control circuit 106 includes a blocking circuit 105 that inputs the voltage across the pair of main terminals of the rectifying MOSFET 101, to block power supply to the control circuit 106 when the inputted voltage across the pair of main terminals is higher than or equal to a first voltage, and to unblock power supply to the control circuit 106 when the inputted voltage across the pair of main terminals is lower than the first voltage.