A magnetic device includes a cylindrical portion and a flange portion. The cylindrical portion is mounted with a cylindrical shaped flexible sleeve. The sleeve is axially longer than the cylindrical portion and includes an outer peripheral concavo-convex portion. When one end of the sleeve is abutted on a flange portion, the other end of the sleeve is projected above an attractive surface to form a keeper housing recess. The sleeve is relatively moved in an axial direction of the magnetic device to be inserted into and removed from a top end of the cylindrical portion. The magnetic device is used under condition the sleeve is fitted, an outer side surface of the magnetic device including the outer peripheral concavo-convex portion of the sleeve and the flange portion abutted on the one end of the sleeve is embedded in a denture base, and the keeper housing recess is exposed.
