Disclosed is a method of analyzing an interference fringe, with which method the optical characteristics of an optical system to be examined can be analyzed very precisely. In one preferred form of the invention, the analyzing method includes a step of detecting information related to a first interference fringe produced by interference of two light fluxes, a step of detecting information related to a second interference fringe produced while changing a phase of one of the two light fluxes by .pi. as multiplied by an odd number (e.g., 1.pi., 3.pi., . . . ), and a step of detecting averaged information of phase information of the two interference fringes, on the basis of the detected information of the first and second interference fringes and by use of Fourier transform.