A projection optical system includes: a refracting optical section composed mainly of a plurality of lenses disposed in order from a reducing side, and having positive power; a first reflecting optical section having a concave reflecting optical surface; and a second reflecting optical section having a convex reflecting optical surface, wherein the projection optical system satisfies the following conditional expression, denoting a focal length of a total system combining the refracting optical section, the first reflecting optical section, and the second reflecting optical section as F, and a focal length of the refracting optical section as FL: 0.2