1. A projection optical system that projects from a first image plane on a reducing side to a second image plane on an enlargement side, comprising:a zoom optical system that includes a plurality of lenses and forms light incident from the reducing side via a first intermediate image formed inside the zoom optical system into a second intermediate image on the enlargement side, the zoom optical system including multiple lenses arranged on the reducing side of the first intermediate image and being configured to correct aberrations including curvature of filed, astigmatism and comatic aberration and multiple lenses arranged on the enlargement side of the first intermediate image and being configured to correct distortion including keystone distortion;
a reflective optical system that includes a first reflective surface with positive reflective power that is positioned closer to the enlargement side than the second intermediate image,
wherein the zoom optical system includes, in order from the reducing side, a former group, a middle group, and a latter group, the latter group including a first lens and a second lens and the first intermediate image being formed therebetween, and
when zooming from a wide angle end to a telephoto end, the former group moves from the reducing side to the enlargement side, the middle group moves so as to compensate for movement of the former group, and the latter group is fixed,
wherein the zoom optical system consists of the former group, the middle group and the latter group, distances between lenses included in the former group are fixed during zooming, and distances between lenses included in the middle group are fixed during zooming.