A method includes preparing a first substrate member in which a cavity is formed. Moreover, the method includes preparing a magnetic member having a plurality of magnetic pieces. The magnetic member is placed in the cavity, and the second substrate member is placed on the first substrate member to close the cavity. The cavity is defined at least in part by a pair of wall surfaces facing each other in a lateral direction and opens upward in an up-down direction perpendicular to the lateral direction. The magnetic pieces are coupled with each other by positioning members so as to be arranged at regular intervals in a predetermined direction. The placing of the magnetic member in the cavity is carried out so that the predetermined direction coincides with the lateral direction or a front-rear direction perpendicular to both of the lateral direction and the up-down direction.