A projection aligner comprises a projection optical system for radiating a luminous flux including ultraviolet rays onto a photomask, and projecting said luminous flux which has passed through the photomask onto a substrate to which photoresist is applied; a substrate table for mounting the substrate, and a light blocking means for covering the peripheral portion of the substrate to block luminous flux. The light blocking means (80) includes a first light blocking member (84) and a second light blocking member (86) each having a substantially semicircular opening, and moving means (82, 83) for moving the first light blocking means and the second light blocking means approaching each other and away from each other. As the first light blocking member and the second light blocking member are moved to approach each other, the first light blocking member and the second light blocking member form an annular shape and cover the peripheral portion of the substrate (CB).
