There is provided an electronic control unit capable of detecting an abnormality of a dark current while suppressing increase in the size of a circuit. The electronic control unit includes a control unit that operates with a current supplied via a power-supply input terminal from a battery, and a diode arranged on a power supply path connecting the power-supply input terminal with the control unit and serving as a reverse connection protection element that prevents a reverse current when the battery is reversely connected to the power-supply input terminal, and detects an abnormality of a dark current flowing through the diode based on a voltage difference between a voltage on the power-supply input terminal side of the diode and a voltage on the control unit side.