A unit plate, which holds electric circuit components including power supply terminals, is secured to a housing cover, which is, in turn, connected to a housing to close an opening of the housing. The housing cover includes guide walls, which extend in a direction generally parallel to a fitting direction of an external connector to guide the unit plate in such a manner that a second end of each power supply terminal held by the unit plate is received in a connector housing part of the housing cover, which is connected with the external connector, at time of installing the unit plate to the housing cover. The unit plate includes a rotation support arrangement, which rotatably supports a rotator. The electric circuit components also include stationary contact members, each of which includes a contact section that is slidably engageable with a movable contact of the rotor.