A determination circuit including a detection circuitry, a switch controller, and a determination circuitry. The detection circuitry is configured to detect that an overvoltage has occurred in an electric power supply path. The switch controller is configured to turn off a switch when the detection circuitry has detected that the overvoltage has occurred. The determination circuitry is configured to perform a determination operation including determining whether the overvoltage that has occurred is attributed to an electric power conversion circuit or a load, on a basis of one of or both a first voltage of a first path and a second voltage of a second path that are in a period in which the switch is off, the first path coupling the switch and the electric power conversion circuit in the electric power supply path, the second path coupling the switch and the load in the electric power supply path.