A position measuring apparatus consists of light receiving means in which a plurality of light receiving devices linearly arranged at an equal interval in the one-dimensional case are grouped so that each group includes the same number of light receiving devices and light source means for radiating light on this light receiving means. A single light source system, a plural light source system, a slight difference system, an interference system and an interference slight difference system which are respectively different in the constitution of this light source means are provided. Signals output from grouped corresponding light receiving devices in the respective groups are added and the periodic function is obtained by arranging this added result at an equal interval. The relative position of light receiving means and light source means in actual space can be precisely obtained by calculating the phase of this periodic function.