Patent ID: 7059723

Claim:
An illumination optical system, which illuminates an image display element, comprising: a light dividing optical system, which divides illumination light flux emitted from a light source into a plurality of light flux portions; and a homogenizing optical system, which illuminates said image display element by using the plurality of light flux portions in such a way that said image display element is illuminated with light having substantially homogeneous intensity distribution, wherein the homogenizing optical system has plural lenses including at least one positive lens and at least one negative lens, wherein a lens out of the plural lenses, closest to said light dividing optical system is a first lens and a positive lens, and wherein the following condition is satisfied: −2≦( R 1+ R 2)/( R 1− R 2)≦−1 where R 1 is a radius of curvature of a surface of the first lens on the light dividing optical system side and R 2 is a radius of curvature of a surface of the first lens on the image display element side.