PURPOSE: To make easy the engagement in the desired location on the wall by boring a through hole at the center of a cylindrical permanent magnet, providing a ferromagnetic protrusion within the through hole while covering the one surface with a ferromagnetic plate, forming a ferromagnetic protrusion also on the opposing ferromagnetic plate and providing leg pieces for engagement at the outer sides of respective ferromagnetic plates.

CONSTITUTION: A through hole 1a is bored at the center of a cylindrical permanent magnet 1 passing from the one magnetic surface to the other magnetic surface, a circular ferromagnetic plate 2 is attached to the one magnetic polar surface and these are accommodated within a non-magnetic cylindrical case 5 having a circular hole at the center of bottom. A ferromagnetic protrusion 2a is fixed by caulking through a fixing bottom metal 4 onto the ferromagnetic plate 2 exposed within the hole 1a by utilizing the circular hole of case 5, and a ferromagnetic plate 3 having the ferromagnetic protrusion 3d at the lower surface opposing to such protrusion 2. At the outer side of ferromagnetic plates 2 and 3, the leg pieces 4a of which free ends are sharpened are provided respectively. The one leg piece 4a is buried within the wall, while the other leg piece 4a is used for engagement of substance, and the protrusion 3a is engaged with 2a during use.