An optical system (L0) that forms an image of an object and that includes an aperture stop (SP), a first reflection surface (R2), and a second reflection surface (R3) which are disposed in order from an enlargement side to a reduction side, an area of the first reflection surface is larger than an area of the second reflection surface, a reference axis is a path of a reference ray that passes through an opening center of the aperture stop to reach a center of a reduction plane, and an angle ∠QPR (deg) between a line segment PQ connecting the opening center P and an intersection Q of the reference axis and the first reflection surface, and a line segment PR connecting the opening center P and an intersection R of the reference axis and the second reflection surface satisfies a predetermined condition.