PURPOSE: To obtain a linear displacement detector in which hysteresis and distortion of output voltage due to axial shift of permanent magnet can be suppressed.

CONSTITUTION: Perpendicularly crossing pectinated pattern of ferromagnetic magnetoresistive element 2 is formed on the surface of a glass substrate, which is subsequently mini-molded with an insulating resin into a rectangular parallelopipedon thus obtaining a magnetism detecting element 1. The ferromagnetic magnetoresistive element 2 formed on the surface of the glass substrate is provided with a magneto-sensitive surface 3. A columnar permanent magnet 6 has square cross-section with pole faces being provided on the opposite end faces thereof. The permanent magnet 6 is arranged movably in the direction of long axis lying on the extension surface of the magneto-sensitive surface 3 which crosses perpendicularly with one side wall face of the columnar permanent magnet 6.