Disclosed is a method of measuring aberration of a projection optical system, that includes an illuminating step for illuminating a reticle by use of light from a light source and through an illumination optical system, a projecting step for projecting an image of a test pattern formed on the reticle, upon a substrate through the projection optical system, a measuring step for measuring a positional deviation amount of the image of the test pattern, and a determining step for determining the aberration of the projection optical system on the basis of the positional deviation amount measured at the measuring step, wherein the projecting step includes a shaping step for shaping the light by use of shaping means disposed in one of the illumination optical system and the projection optical system and a light blocking pattern formed on a surface of the reticle, remote from a surface of the reticle where the test pattern is formed, so that the light passes only through a predetermined region of a pupil of the projection optical system.