A projection display system comprising a projection display unit including a light source, an image display element, a lighting optical system irradiating a beam of light on the image display element, and a projection optical system projecting an image light from the image display element toward a screen. The projection optical system including a lens group composed of a plurality of lens elements arranged in order toward the screen from the image display element and symmetrically with respect to an optical axis, and a reflecting mirror shaped to be axial-asymmetrical with respect to the optical axis. The projection display system further comprises a screen 5. The projection display unit projects the image light onto a projection plane of the screen to display an image.