PURPOSE: To provide an apparatus which can measure both the rotation angle and the revolution speed simultaneously.

CONSTITUTION: A slit plate 4 in which a light transmissive and divided slit is formed at a distance from a rotary center corresponding to a rotational angle is installed and a light source 5 and a light position detecting element 1 are also installed while having the slit plate 4 between them and the rotation angle is computed from the wave height of an analog output sent out of the light position detecting element 1 and the rotational speed is computed from the cycle or frequency of the pulsed output.