ROTATION ANGLE DETECTOR

PURPOSE:To provide the rotation angle detector where the output voltage of a photodetector is proportional to the angle of rotation of a light shielding plate and the dark current of the photodetector is small and the rotation angle detection precision is high. CONSTITUTION:A rotation angle detector 10 is provided with a photo sensor unit 4 consisting of a light emitting element 4a and a light receiving element 4b facing each other with a gap 5 as the optical path between them and a light shielding plate 3a, which is attached to a revolving shaft 1 and has a light shielding end shaked and turned in the gap 5, and detects the angle of rotation of the revolving shaft 1 by the output of the light receiving element 45 which is obtained at the time of intercepting the light from the light emitting element 4a by the light shielding plate 3a, and the gap 5 is arranged in parallel with the axis of rotation of the revolving shaft 1, and the light shielding plate 3a is arranged in the gap 5 in parallel with the axis of rotation of the revolving shaft 1 and has the light shielding end made parallel with the axis of rotation of the revolving shaft 1.