PURPOSE: To miniaturize and lighten a magnet part, magnetism thereof is shielded, by affixing a magnetic shielding plate consisting of specific thickness and width onto an at least pole face.

CONSTITUTION: A pole-contact plate 2 is appended to one pole face (a) of a permanent magnet 1 and a plate 3 to the other pole face (b) in a shielding manner, and the thickness of the shielding plate 3 extends over 0.04W1.00mm. The pole-contact plate 2 mounted to the pole face (a) of the permanent magnet 1 is extended up to a section such as the side of the pole face (b) while a clearance (d) sufficient for preventing the short circuit of the magnetic line of force is interposed between the plate 2 and a circumferential wall (c) extending over the pole faces (a), (b) of the permanent magnet 1. The magnetic line of force focused to the shielding plate 3 is collected to the extended pole-contact sections 2a, 2a as one of paths having least reluctance, thus generating strong sucking force on the upper end of pole-contact plate section 2a. The magnetic line of force changes the pole-contact plate section 2a into a magnetic path, thus preventing the leakage of the magnetic line of force to the outside of the circumferential wall (c) of the permanent magnet 1, then attaining effective magnetic shielding.