An optical displacement measuring system utilizing a triangulation is so arranged that light receiving means receives light reflected back from an object to be measured and generates a pair of output signals having mutually opposite values and responsive to a position of a light spot on the light receiving means. An operational means performs addition and subtraction over the pair of positional output signals and to obtain a ratio between the both added and subtracted output signals for generating a measured distance signal, and a linearity correcting means provides a mathematical correction number to one of the pair of positional output signals to correct any nonlinearity of the measured distance signal, for providing the linearity to the measured distance signal with a simple arrangement.