a stator portion including an armature;

a rotor portion including a shaft concentric with a central axis, a rotor core having a substantially cylindrical shape arranged to surround the shaft, and a field magnet which is arranged at the rotor core and which, along with the armature, generates a torque centered about the central axis;

a bearing mechanism arranged to rotatably support the rotor portion with respect to the stator portion centered about the central axis, the bearing mechanism including a first bearing portion and a second bearing portion respectively arranged at a first axial side and a second axial side of the rotor core to support the shaft in a rotatable manner;

a sensor arranged at an axial side of the armature to magnetically detect an angular position of the rotor core with respect to the stator portion; the sensor including:

a yoke having a substantially annular share, made of a magnetic material and arranged at the shaft;

a sensor magnet having a substantially annular share arranged at the yoke;

a magnet cover made of a nonmagnetic material covering a surface of the sensor magnet other than a portion thereof in contact with the yoke; and

a Hall element arranged opposite from the yoke with respect to the sensor magnet;

a housing arranged to accommodate therein the stator portion and the rotor portion, the housing including a housing body having an opening at an axial side thereof; and

a lid portion arranged between the armature and the sensor magnet so as to retain the first bearing portion and close the opening of the housing body.