PURPOSE: To obtain an optical angle sensor characterized by accurate detection of the rotary angle of a shaft, a low cost and easy assembling, by providing a disk having an elliptical reflecting pattern and an optical reflection sensor having an elliptical sensor region.

CONSTITUTION: An optical reflection sensor 8 is composed of a light emitting element 9, first and second optical fibers 11a and 11b and a light receiving element 10. The light from the light emitting element 9 is guided to a pattern disk 6. The reflected light is detected by the lighr receiving element 10 and outputted. Based on the change in amount of the reflected light, the rotary angle of a pattern disk 6 is detected. Namely, a pattern 7 on the pattern disk 6 is overlapped with a reading spot 12 of te optical reflecting sensor 8 as shown in the Figure. The overlapped part 16 is a region where the reflected light can be read. The area of the reading part is changed in correspondence with a relative angle θ between the spot 12 and the pattern 7. Thus the output corresponding to the angle θ is obtained.