An electronic control unit of one embodiment includes first and second microcomputers for mutually monitoring operations, an output circuit for outputting a signal that is outputted from at least one of the first and second microcomputers, a power supply circuit for supplying electric power to the output circuit, and a stop unit for stopping supply of the electric power from the power supply circuit to the output circuit. The first microcomputer has operation modes including a normal mode and a low power mode. In the low power mode, the first microcomputer stops monitoring the operation of the second microcomputer and outputs a power supply stop signal that operates the stop unit to stop the supply of the electric power from the power supply circuit to the output circuit.