A magnet plate includes a regulating member which is adapted to be press-fitted to a blind hole of a base plate. The regulating member protrudes from the surface of the base plate at one end, and prevents a permanent magnet from moving in a transverse direction. The regulating member has a narrower portion having a width smaller than the blind hole. Upon press-fitting of the regulating member, the base plate undergoes plastic deformation and the deformed portion moves into a space between the narrower portion and the inner wall of the blind hole.