A wavefront aberration measuring apparatus which measures an wavefront aberration of an optical system to be inspected includes a point light source which supplies a measuring light; a photodetector which has a detection surface arranged at a position optically conjugate with the point light source; a wavefront change applying section which is arranged in an optical path between the point light source and the photodetector and which applies a wavefront change to the light outcome from the optical system; and a measuring section which measures the wavefront aberration of the optical system based on an output of the photodetector and the wavefront change applied by the wavefront change applying section. It is possible to measure the wavefront aberration of the optical system with a relatively simple construction, without using the interference method.