PURPOSE:To read the minute shape of a material to be measured directly in numerical values, by providing a first interferometer, which inputs a light beam into a three-division beam splitter; a second interferometer; a supporting device for the material to be measured, which displaces the material to be measured along an x axis; and light detectors, which count the changes in frequencies of the first and second interference beams, which are transmitted through or reflected by the three-division beam splitter. CONSTITUTION:An optical system 1 is provided with the following parts: a three-division beam splitter 22; a first interferometer 23, which projects one beam on the surface of a material to be measured 3 and measures the height of the material (coordinate on a z axis); and a second interferometer 24, which projects another beam on a cube corner prism 18 and measures the measuring position of the height (coordinate of an x axis). The material to be measured 3 is mounted on a mounting table 17 and a laser beam 25 is projected from a laser light source 21. Then, unevenness of the material to be measured 3 is measured in relation to the position, based on the interference of the laser beams in the interferometers 23 and 24.
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