PURPOSE: To detect the position and movement quantity of a magnetic detector with high sensitivity by moving integrally two magnetic detectors which are supported at an interval a half as large as the interval between two adjacent magnets.
CONSTITUTION: Every two permanent magnets 2 and 3 are arranged alternately at both end parts and intermediate parts of magnetic plates 11 and 12 to constitute a closed magnetic circuit 13, and three divisions of length (l) are obtained by the magnets 2 and 3 at the intermediate parts. Further, a carrier 22 which is movable in the lengthwise directions of the closed magnetic circuit 13 across the magnets 2 and 3 arranged at the intermediate parts of the closed magnetic circuit 13 and a couple of magnetic detectors 8a and 8b which are mounted on the carrier 22 are provided so that their interval is l/2 in the length direction of the closed magnetic circuit 13. For the purpose, the intensity in the leak magnetic field 9 in the closed magnetic circuit 13 is detected by the detectors 8a and 8b and then the detection voltages outputted by the detectors are l/2 out of phase with each other. Then, only parts of both output voltages which have superior linearity are extracted and utilized to obtain a high-performance positioner.