To provide an apparatus which detects rotation of a rotating body without a power source and at low cost.

According to the rotation of a motor, a magnetic path is formed by a magnetic detector 24 or 26 (more precisely, magnetic wire 70), magnetic poles of a magnet 22 facing the detector, and a rotating shaft 20. Since the magnetic wire 70 is composed of a magnetic body which probably causes large Barkhausen jump, the direction of magnetic field forming the magnetic path switches steeply at every switching of the magnetic pole facing each magnetic detector in response to the rotation of the motor, so that pulse signals responding to the switching are output from the magnetic detector. Since the magnetization direction of the magnet 70 switches according to the change of magnetic flux received from the magnet 22, an induced electromotive force by the change of magnetic flux which the detecting coil receives, is generated, and the pulse signals are output from the magnetic detector without a power source.