A thin plate 80x forming a stator tooth 80 has two convex portions 83 on each of side faces 80b, 80c. Four convex portions 83 are a sharpened convex portion 83a of which a tip portion has a thickness thinner than a thickness of the thin plate 80x. When a bobbin 81 wound with an exciting coil 22 is press-fitted around the stator tooth 80, four lines of convex portions formed by laminating the thin plates 80x cut in an inner wall of the bobbin 81, the strength for fixing and holding the bobbin 81 can be increased in a radial, lamination and rotating directions, so that the position of the bobbin 81 assembled in a right position can be maintained.