A projection optical system includes a first refracting optical system having a plurality of lenses, a first reflecting optical system, and a second reflecting optical system. The first reflecting optical system is disposed on a side of a projection port with respect to an optical axis of the first refracting optical system, and has a positive optical power to reflect light incident through the first refracting optical system in a direction opposite to the side of the projection port. The second reflecting optical system is operable to reflect the light reflected on the first reflecting optical system toward the projection port.