A photointerruptor for use in an optical transmission-type rotary encoder comprising a rotatable pulse scale having a code pattern and a light-emitting optical fiber and a light-receiving optical fiber secured to a housing with their end faces being opposed to each other on both sides of the code pattern. The housing has a housing main body a pair of optical fiber opposing members for previously inserting the top ends of the respective optical fibers and a housing main body having fitting recesses for holding the optical fiber opposing members with the end faces of the optical fibers being opposed to each other at a predetermined distance on both sides of the code pattern. The housing main body may be constituted by a pair of optical fiber opposing members engageable with each other.