Abstract: An optical encoder comprising a photointerruptor having light-emitting and light-receiving optical fibers and a rotatable pulse scale disposed in an optical path between both of the opposed end faces of the optical fibers so as to shut the optical path intermittently, thereby generating optical pulses in accordance with an angle of rotation of the pulse scale, in which the light-receiving optical fiber has a larger diameter and a greater numerical aperture NA than those of the light-emitting fiber. The light-emitting optical fiber may be replaced with a light-emitting device. Further, a reflector may be interposed in the optical path. Optical pulse signals indicative of an angle of rotation can be detected effectively and it is possible to facilitate the assembling or wiring operation and reduce the production cost.