The present invention is provided with a heat dissipation base 23 that is adjacent to an electric motor unit EM and extends, near a rotational shaft of an electric motor, in a rotational shaft direction. A substrate 24 of one electronic control means of a redundant system is fixed, in a manner of allowing heat conduction, to the heat dissipation base 23, along the direction in which the heat dissipation base 23 extends. A substrate 26 of another electronic control means is fixed, in a manner of allowing heat conduction, to the heat dissipation base 23, so as to face the substrate 24 of the oneelectronic control means. Heat from the substrate 24, 26 of each electronic control means dissipates to a motor housing 20 via the heat dissipation base 23. Additionally, a rotational position detection circuit substrate 22, to which neutral terminals 31 of each phase of the electric motor are respectively connected, is provided between the heat dissipation base 23 and the motor housing 20.