To acquire the information for a moving object with precision by providing a magnetic field distorting means between the object and the end surface of a facing permanent magnet, with a magnetic field sensor means provided on its upper surface.

A cylindrical permanent magnet 12 provided in a cylindrical wall 14 comprises an axial center 18 and a magnetic pole surface 20. A magnetic flux rod 22 is fitted to the magnetic pole surface 20, and magnetic field sensor elements (referred to as element) 24 and 26 are fitted to its upper surface 28. The elements 24 and 26 comprise a thin-film base part 30, with a positive and negative poles on upper side while terminals 32, 34, and 36 on ground side. A device 10 is positioned against a magnetic-conductive body such as a rod R. The gap of the rod R between a land 50 and a slot 52 is proportional to that between the elements 24 and 26. Providing the magnetic flux rod 22 causes the magnetic field of the permanent magnet 12, and the magnetic flux line in the element terminal parts 32 and 34 region is constrained to such direction as across a motion direction 48 of the object for balancing of magnetic field. As a result, the reading precision from an sensor is improved.