There is provided a projection optical system for projecting a pattern on an object surface onto an image surface in a reduced size. The projection optical system includes six reflective surfaces that includes, in order of reflecting light from the object surface, a first reflective surface, a second convex reflective surface, a third convex reflective surface, a fourth reflective surface, a fifth reflective surface and a sixth reflective surface, and an aperture stop along an optical path between the first and second reflective surfaces.