PURPOSE: To perform stable detecting operation without using any magnetoelectric conversion element nor magnet having high sensitivity and strong magnetic force, but with a generally used magnetoelectric conversion element or a magnet.

CONSTITUTION: Two magnets 21 and 22 fixed at a prescribed interval in a facing state are connected to each other by means of a magnetic material put between the magnets 21 and 22. A rotating shaft 24 is connected to the magnetic material 23 so that the shaft 24 can support the magnet unit 2 composed of the magnets 21 and 22 and the material. 23 in a rotatable state. A magnetoelectric conversion element 6 is provided near the unit 2 and generates a prescribed number of pulses based on the magnetic field produced by the two magnets 21 and 22.