An interfitting groove is disposed in a bottom portion of a trough portion so as to have a groove direction that is axial and so as to extend axially outward from axially inside, and a rotation arresting portion housing recess portion is recessed into an axially inner opening edge portion of the interfitting groove on a first yoke portion. A magnet holding seat that holds a permanent magnet is disposed in the trough portion by an interfitting portion being fitted into the interfitting groove such that radial movement is restricted. A rotation arresting portion that is disposed so as to project axially outward from a flange portion of the bobbin is housed inside a space that is constituted by the rotation arresting portion housing recess portion and an external shape reduced portion that extends axially inward from the interfitting groove such that rotation of the bobbin around the shaft is restricted.