As shown in FIGS. 2 and 3, each of the magnetic pieces 141 has a rectangular board shape. In the present embodiment, the magnetic pieces 141 are formed so as to have the same shape and the same size as each other. Moreover, the magnetic pieces 141 are arranged at predetermined intervals in a predetermined direction so that long edges of the magnetic pieces 141 are parallel to one another. In order to realize the arrangement, the magnetic pieces 141 are coupled with each other by positioning members 143. A space between adjacent two of the magnetic pieces 141 works as a gap in a magnetic circuit. Accordingly, the predetermined intervals should be decided according to magnetic characteristics required for the magnetic member 14. The predetermined direction is a direction which is decided freely. In the present embodiment, the predetermined direction coincides with the lateral direction.

As shown in FIGS. 2 and 3, in the present embodiment, adjacent two of the magnetic pieces 141 are coupled with each other by two of the positioning members 143. Each of the positioning members 143 couples one surfaces of adjacent two of the magnetic pieces 141 with each other. In detail, each of the positioning members 143 couples surfaces, which face each other, of adjacent two of the magnetic pieces 141 with each other. However, the present invention is not limited thereto. The magnetic pieces 141 adjacent to each other should be coupled with each other by at least one positioning member 141.