An exposure apparatus which includes a projection optical system that projects a pattern image of a reticle onto an object to be exposed, and an interferometer configured to measure an optical characteristic of the projection optical system. The interferometer includes a mask placed on an object plane side of the projection optical system, the mask shaping a wavefront of light from a light source into an ideal wavefront, a detector configured to detect the light passing through the projection optical system; and an optical element placed between the mask and the projection optical system or between the projection optical system and the detector. The detector detects interference fringes (an interferogram) formed by interference between a reflected component of the light reflected by the optical element and a transmitted component of the light passing through the optical element.