A method of exposing images of measuring patterns formed on a mask on a photosensitive substrate through a projection optical system, measuring positional deviation quantities of the exposed images of the measuring patterns in a measuring direction and thus measuring imaging characteristics of the projection optical system on the basis of the measured positional deviation quantities. In this method, periodic patterns are used as the measuring patterns, wherein bright and dark portions are arranged at a predetermined pitch in a direction corresponding to the measuring direction. The positional deviation quantity is measured by assuming the image of the periodic pattern as an image of the pattern consisting of the single dark portion on the whole when measuring the positional deviation quantity of the periodic pattern image exposed on the photosensitive substrate in the measuring direction. The mask may be formed with measuring marks in which a plurality of pattern units consisting of periodic patterns having bright and dark portions arranged at the predetermined pitch are arranged in lattice at an interval larger than the predetermined pitch.