PURPOSE: To improve the detection sensitivity and to enable the miniaturization of the titled detector, by providing a magnet, two magnetic pole pieces being in contact with said magnet and magnetized to be different magnetic poles from each other, and a magnetism detector detecting a change in magnetic flux caused by the above components.

CONSTITUTION: A rotation detector 10 is composed mainly of a rod-shaped magnetic pole piece 11 formed of a magnetic substance, a hollow cylindrical case 12 formed also of a magnetic substance and opened at both ends, a cylindrical magnet 13 the center of which is pierced through by the magnetic pole piece 11, which is inserted through the center of the case 12 approximately and which is magnetized in the radial direction so that the central and outer-peripheral parts thereof become poles different from each other, and a coil 14 wound on the outer-periphery of one end part of said magnetic pole piece 11. By such a constitution, magnetic refluctance can be reduced so as to enlarge a change in magnetic flux accompanying a change in a magnetic gap, and thereby an improvement in the detection sensitivity and the miniaturization of the device can be attained.