An electronic control unit monitors a state of a monitor target based on an analog signal from a sensor which is supplied with electric power and which outputs the analog signal that changes in accordance with a value of the electric power and the state of the monitor target. The electronic control unit includes a first power supply, a second power supply having higher accuracy than the first power supply, and a controller. The controller supplies the power to the sensor with the first power supply and determines whether there is a change in the state of the monitor target based on the analog signal. When determining that there is the change, the controller switches over a power supply from the first power supply to the second power supply and determines whether there is a change in the state of the monitor target.