An illumination unit comprising a light source having an arc tube and an ellipsoid reflector, a concave lens having a light incident surface of hyperboloid of revolution for substantially parallelizing an illumination light beam from the light source, a first lens array, and a second lens array, characterized in that a concave surface exists between the light incident surface of the concave lens and the surface of the first lens array on which a plurality of micro lenses are formed and has a function of allowing, in cooperation with the light incident surface of the concave lens, the illumination light beam having passed through the light incident surface of the concave lens to travel along an optical path extending outward from the optical path parallel to the optical axis of the light source and to pass through corresponding micro lenses of the first and second lens arrays. The loss in the quantity of light can thereby be reduced and the utilization efficiency of the illumination light beam can be enhanced. |