A noncontact type rotation sensor, which can detect the rotational movement of a gear with high sensitivity and precision without causing any erroneous output, is disclosed. To a magnetic gear is applied a bias magnetic field by a bias magnet from the direction of the teeth of the gear. A sensor part disposed within the bias magnetic field comprises a substrate and a plurality of magneto-resistive elements mounted on the substrate in parallel to the teeth of the gear and electrically connected in series one after another. The sensor part detects the magnetic vector of the bias magnetic field varying according to the rotation of the gear as the composite value of the variations of the resistance values of the plurality of magneto-resistive elements connected in series one after another. The plurality of magneto-resistive elements are arranged with interval and width that enable the plurality of magneto-resistive elements to absorb the erroneous output caused to the variation waveforms of the respective resistance values during power supply.