INTERFERENCE MEASUREMENT

PROBLEM TO BE SOLVED: To provide an interference measurement device capable of performing, by using one optical system, measurement for obtaining the fine structure of a specimen surface and measurement for obtaining the phase distribution of a moving specimen.SOLUTION: The interference measurement device includes reference mirror moving means for performing phase shifting by moving a reference mirror 26 by λ/n (λ is wavelength, and n is natural number of 3 or more) along an optical axis from reference position, reference mirror rotation means for rotating the reference mirror 26 around a rotary shaft orthogonal to an optical axis Z, an image pickup device 16 irradiated with an interference light flux combined by PBS8 to image an interference fringe pattern according to the phase distribution of a specimen surface 11 for each phase shifting, and an analyzer 31 for calculating the interference fringe pattern obtained for each phase shifting by using a phase shift interference method to reproduce the phase state of the specimen surface.