a semi-transmitting/reflecting surface that reflects part of a light beam to be measured back in the opposite direction to the direction of incidence as a sample luminous flux;

a reference light producing device, which has a converging lens that converges a transmitted luminous flux transmitted through said semi-transmitting/reflecting surface, and a minute reflection diffracting part disposed at the convergent point of said converging lens, and converts part of said transmitted luminous flux incident thereon from said semi-transmitting/reflecting surface into a wavefront-shaped reference luminous flux, and outputs said reference luminous flux toward said semi-transmitting/reflecting surface; and

an image-forming part that has a detection surface, and leads, to said detection surface, interfering light obtained by combining said reference luminous flux and said sample luminous flux, so as to form interference fringes on said detection surface;

wherein the wavefront-measuring interferometer apparatus is constituted to carry out wavefront measurement on said light beam based on said interference fringes formed on said detection surface.