The invention includes a base member attached to a casing. The inside of the casing can be a vacuum atmosphere. A partition wall is provided on the base member, the base member separating an air atmosphere and the vacuum atmosphere. A rotating member (a rotating portion of a driving source) is provided on the base member at a position different from the rotating member. An armature, which is a dust source, is provided on the air atmosphere side of the partition wall, thereby maintaining high cleanliness on the vacuum atmosphere side. Providing the partition wall and the rotating member at different positions eliminates the necessity of consideration on the rigidity of the partition wall for supporting the rotating member, thereby reducing the thickness of the partition wall. In addition, it is possible to reduce affection by deflection generated by the inertia or vibration caused by rotation of the rotating member, so that a distance between the armature and a magnet in the rotating member can be narrower than the related art. Accordingly, high accuracy in stopping positions can be realized.