An 8-mirror reflecting type projection optical system. A first reflecting image forming optical system forms an intermediate image of a first surface and a second reflecting image forming optical system forms an image of that intermediate image on a second surface. The first reflecting image forming optical system has a first reflecting mirror M1, a second reflecting mirror M2, a third reflecting mirror M3, and a fourth reflecting mirror M4. The second reflecting image forming optical system has a fifth reflecting mirror M5, a sixth reflecting mirror M6, a seventh reflecting mirror M7, and an eighth reflecting mirror M8. The first reflecting mirror M1, the fourth reflecting mirror M4, the fifth reflecting mirror M5, and the eighth reflecting mirror M8 have concave reflecting surfaces, and the seventh reflecting mirror M7 has a convex reflecting surface. One of the second reflecting mirror M2 and the third reflecting mirror M3 has a concave reflecting surface, and the other has a convex reflecting surface. The width dimension of an arcuate effective image forming region is relatively large.