Abstract: A photoelectrically readable digital micrometer for precisely measuring a micro distance includes an outer ring having a micro internal thread, a spindle shaft having an external thread screwed into the internal thread, a disc-shaped scale plate having a scale provided around the periphery of the plate surface, the scale plate being secured to the spindle shaft perpendicular to the plate surface, a slidable ring slidably mounted on the outer ring and being slidable in the axial direction together with the spindle shaft, and a light source member and a light receiving member secured to the slidable ring and sandwiching the scale of said scale plate.