A magnetic device 2 has a cylindrical portion 22 and a flange portion 23. The cylindrical portion 22 is mounted with a sleeve 4 having flexibility and formed in a cylindrical shape. The sleeve 4 is axially longer than the cylindrical portion 22 and has an outer peripheral concavo-convex portion 44. When one end part 41 of the sleeve 4 is abutted on a flange portion 23, the other end part 42 of the sleeve 4 is projected above an attractive surface 25 to form a keeper housing recess 49. The sleeve 4 is relatively moved in an axial direction of the magnetic device 2 to be inserted into and removed from a top end of the cylindrical portion 22. The magnetic device 2 is used under the condition that the sleeve 4 is fitted, an outer side surface of the magnetic device 2 including the outer peripheral concavo-convex portion 44 of the sleeve 4 and the flange portion 23 abutted on the one end part 41 of the sleeve 4 is embedded in a denture base 82, and the keeper housing recess 49 is exposed.
