To stably project and expose a fine pattern, based on proper image forming performance by checking the deterioration of the image forming performance of an immersion-type projection optically system due to replacement of a light-permeable member in the immersion region.

The aligner has a projection optical system for forming a pattern image of an object surface on a photosensitive substrate via a liquid in an immersion region formed on the image surface side. The light permeable member in the immersion region of the projection optical system is replaceable with a replacing light-permeable member (Ha, Hb) to be disposed in the immersion region. According to the replacement of the replacing light-permeable member, the optical path length of the immersion region in the projecting optical system is made adjustable.

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