To impart very high anisotropy to a shield rate along an orthogonal axis by the structure, wherein the loop-shaped rings of a soft magnetic material having high permeability are separated by the coaxial spacer rings of non- magnetic material partially containing air.

A basic structure 20 of an anistropic shield structure comprises a plurality of N pieces of loop-shaped rings 22 of soft magnetic material having high permeability. The rings 22 are mutually separated by the series of N-1 pieces of spacers 24 of ordinary non-magnetic material (containing air). When the above described structure is formed, for example, 14 pieces of the loop- shaped rings 22, whose permeability μ is in the order of 104, are used in the structure 20, wherein the length L is about 1.3 inches and the diameter D is about 1 inch. The shield rate in the radial direction is in the order of several hundreds, and the shield rate in the axial direction is about 1. For example, the suitable magnetic field is applied on the head part of a human body, and the fringe magnetic-field component is detected with the magnetic-field detecting system constituted by using a magnetoresistance sensor and the above described ring-shaped shield structure. Thus, foreign material such as a metal piece can be detected.