When an optical system is illuminated with illumination light fluxes emitted from respective input image points, an interference image generated by superimposing output light fluxes output from the optical system and a reference light flux coherent with the output light fluxes is imaged to acquire interference image data collectively including information of an interference image about all input image points. Diffractive optical light propagation simulation is performed to acquire a phase distribution associated with only light emitted from a single input image point at a position where reconstructed light fluxes to the respective output light fluxes are separated into each light flux. In each input image point, this simulation is performed to acquire a phase distribution on an exit pupil plane.