This specification discloses a measuring apparatus for measuring the wavefront aberration of an optical system for a soft X-ray which can highly accurately measure the wavefront aberration of the optical system without using the soft X-ray. This measuring apparatus has a light source for supplying light of a predetermined wavelength, and a detector disposed at a location whereat an interference fringe is formed by the light of the predetermined wavelength passed through the optical system, and measures the wavefront aberration of the optical system on the basis of the result of the detection by this detector. The predetermined wavelength is a wavelength within a wavelength range of 150 nm to 300 nm.