Disclosed is a projection optical system including a first optical system configured to form a first image conjugate to an object and have an optical axis and a second optical system configured to project a second image conjugate to the first image onto a surface to be projected on, wherein the first image satisfies a condition of: Im×Tr≦1.70 wherein Im denotes a length of the first image in a direction of an optical axis of the first optical system, normalized by a focal length of the first optical system, and Tr denotes a throw ratio for the projection optical system.