To ensure high overlay accuracy even when a projection aligner having a remaining asymmetric random image distortion is used mixedly.

A transparent correction plate 8 is interposed between a reticle R and a projection optical system PL. The correction plate 8 is disposed removably by a replacing unit 21 and replaced, as required, by another correction plate 24a-24c stocked in a stock room 23. The correction plate 8 is polished to correct random distortion in a projection aligner employing it. Furthermore, distortion of a projected image is corrected by selecting the correction plate 8 depending on the image distortion characteristics of a projection aligner 28 used in the preceding exposure step or a projection aligner 29 used in the following exposure step thus enhancing the overlay accuracy between two layers.