To provide a power circuit capable of suppressing the time until electric power supplied to a load circuit is stopped from increasing even when a voltage of an AC power supply becomes higher.

A power circuit 100 includes: a transformer 1 including a primary winding 1a in which a voltage of an AC power supply 200 is input; a diode D1 which compares the magnitude of a voltage to be input into the primary winding 1a of the transformer 1 to that of a voltage based on a full-wave-rectified voltage of the AC power supply 200; an LED 8 to which electric power output from the secondary side of the transformer 1 is supplied; and a photo coupler 5 and a transistor 9 that stop power supply to the LED 8 on the basis of an electric current running through the diode D1.