An adjusting method of an optical system composed plural optical elements each having a multilayer film, said adjusting method that includes a first measuring step that obtains, for each optical element, a difference between a phase distribution of which an EUV light (Extreme Ultraviolet light) is reflected from the optical element and a phase distribution of which a light with a wavelength that is longer than the EUV light is reflected from the optical element, a second measuring step that measures a phase distribution of which the light passes the optical system, a deciding step that decides a phase distribution of which the EUV light passes through the optical system based on the phase distribution difference obtained by the first measuring step and the phase distribution measured by the second measuring step, and an adjusting step that adjusts at least one of a position and a posture of the optical element based on the phase distribution decided by the deciding step.