PURPOSE: To make handling easy and constitution simple by detecting the position of a magnetism generating body consisting of a bar like magnetic piece by the use of a reluctance effect element.

CONSTITUTION: A reluctance effect element 2 has both terminals (a), (b) and a terminal c led out from a central part (c). A magnetism generating body 1 consisting of a bar-like magnet piece is roughly of the same size in length as that of the detecting part of the element 2 and is held magnetized in the direction at a right angle to the element 2. If a difference of the two signals obtd. by flowing a constant electric current to two resistors R1 and R2 of the element 2, the position of the body 1 is detected.