PURPOSE: To prevent a large projection to generate at the side of a line of magnetic force in a magnet by attaching and setting up a magnetic shielding plate to the upper and lower surfaces of the magnet and generating an adsorbing effect by the mounting of a male stud to a magnet surface.

CONSTITUTION: The ferromagnetic plate 2 is brought into contact with one side of the magnetic pole surfaces of the permanent magent 1, in which a hole 1a is formed toward the other side from one side of the magnetic pole surfaces, and the ferromagnetic plate 3 with the other magnetic pole surface except the hole 1a, both plates are fixed and set up integrally by a case 4 consisting of a nonmagnetic blank while a projection 2a up to the upper end of the hole 1a is erected to the plate 2, and the generation of the line of magnetic force to the outer side from the plates 2, 3 is inhibited extremely. The case 4 takes a cylindrical shape consisting of the nonmagnetic blank, a pawl 4b for turn-up is formed at the lower end edge of the case and a turn-up edge collar 4a at the other cylindrical end, the plate 3 is fitted and set up so as to be brought into contact with the collar 4a, a cylinder end thereof is turned in to the inner side, the magnet 1 and the plate 2 are fitted and set up to the plate 3, the pawl 4b is turned in onto the surface of the plate 2, and these members are enclosed integrally into the case 4.