PURPOSE: To prevent magnetic interference to a magnetic recording body, by a method wherein one engaging member with an engaging hole is fitted to an attaching substrate and edge flange projecting from the magnet surface is provided.

CONSTITUTION: An engaging member (a) comprises a permanent magnet 1 with an engaging hole 1a, a ferro-magnetic plate 2 disposed to both surfaces of the magnet 1, and a ferro-magnetic plate 3 with shield edge 3a, 3b. The engaging member (a) is fitted in a non-magnetic case 7 having edge flange 7a inserted to opened portion of a mounting substrate (c). Then the edge flange 7a projects from the magnet surface, i.e. plate 3. In such constitution, the edge flange 7a serves as a protective edge thereby contact of the magnetic recording body to the plate 3 is obviated. Thus magnetic interference to the magnetic recording body is prevented.