Patent ID: 8400641

Claim:
An interferometer that measures the shape of a surface of an inspection object, the interferometer comprising: an interference optical system that splits light from a light source into inspection light and reference light and causes the inspection light reflected by the surface of the inspection object and the reference light to interfere with each other; and a photoelectric conversion element that detects interference fringes produced by the interference of the inspection light and the reference light, wherein the interference optical system includes a first optical element that transmits and reflects the inspection light and has a flat reflecting surface, a second optical element that reflects the inspection light, and a moving unit configured to move the second optical element, wherein the inspection light passes through the first optical element, is reflected by the second optical element, is reflected by the first optical element, and is then incident on the surface of the inspection object, and wherein the inspection light reflected by the surface of the inspection object is reflected by the first optical element, is reflected by the second optical element, passes through the first optical element, and interferes with the reference light.