To provide a method for manufacturing a rotary encoder capable of improving productivity by omitting a centering work of a rotary plate, that is, a regulating work by a manual work.

The method for manufacturing the optical rotary encoder 1 comprises (1) a first assembling step of assembling a rotary shaft 5 and a fixed plate 11 with a base 2, (2) a window forming step of forming a window at the plate 11 and the shaft 5 as a reference position, (3) a second assembling step of mounting a rotary plate 7 at the shaft 5, and (4) a pattern forming step of forming a pattern on the surface of the plate 7 at the shaft 5 as a reference position.