An optical rotary encoder having a rotatable pulse scale having a row of code pattern with specific light-permeable or-deflection slits each for outputting a reference position signal and other light-permeable or reflection slits each adapted to reduce the amount of light for outputting an angular signal, both of the optical signals being photoelectronically converted and the waveform of the resultant electric signals being shaped based on threshold voltages into electric pulse signals indicative of a reference angle of 0 DEG and the accumulated angle of rotation, in which the circumferential width of each specific reference slit is made narrower than that of other slit so that the pulse width for angular position indicating of the angular pulse signal is always equal and constant for ensuring more accurate detection of the angle of rotation.
