An electronic control unit includes a sensor circuit board 30 which is mounted with sensors 33, 34 for detecting a predetermined physical quantity; a control circuit board 20 which controls an operation of an electric component on the basis of the physical quantity detected by the sensors 33, 34; and a housing 40 which accommodates the sensor circuit board 30 and the control circuit board 20, wherein at least one of the sensor circuit board 30 and the control circuit board 20 is mounted to a circuit board support stepped portion 47 formed in an inner surface of the housing 40 so that the sensor circuit board 30 and the control circuit board 20 are arranged in a layered state.