Optical measuring system is located in the generation of parallel light for incidence on the surface and which may be parallel to vary the wavelength of the parallel light generating section, parallel to the light path of the inspection stage body rotates in the predetermined rotation angle in accordance with an exemplary embodiment surface is provided to be parallel to the wavelength of light, and a according to the angle of rotation passed through the parallel light incident angle and rotation grating to change the incident position, respectively, and rotating the grid to the surface of the inspection stage body parallel light is inspection stage body as the incident angle and incident location the incident and may include a collection of reflecting the reflected light to produce collected. Because by varying the wavelength, and rotating the rotating grating can be changed parallel to the incident angle and incident location on the upper surface of the inspection stage, it is possible to inspect the surface of the inspection stage body at a faster rate. A defect detection efficiency of the optical measurement system to increase and it is possible to increase the overall efficiency and productivity of the semiconductor manufacturing process.