A projection optical system for use in a precise copy which uses a pair of catadioptric optical systems (I and II) consisting of convex mirrors (2, 6), concave mirrors (3, 5), and phase correction members (4, 4') is shown. Two catadioptric optical systems (I and II) commonly use an entrance pupil (E, EP) on a coaxis and are coupled so as to respectively face the phase correction members (4, 4'). Each of the concave mirrors (3, 5) has an opening at the center. Each of the convex mirrors (2, 6) has no opening in one embodiment but has an opening portion at the center in another embodiment.