To realize an illumination optical device having high brightness and high uniformity of brightness over a predetermined area, performing illumination excellent in the direction characteristic of luminance and having the high utilization efficiency of light emitted from a light source while realizing miniaturization as an entire illumination device, and to realize an optical device using the illumination optical device.

The illumination optical device is provided with a plurality of light emitting elements two-dimensionally arranged in parallel, a 1st lens array 2 comprising element lenses corresponding to the respective light emitting elements, a 2nd lens array 3 comprising element lenses corresponding to the respective element lenses, and an illumination lens 4. The respective light emitting parts 103 of the plurality of light emitting elements are made to form an image as an enlarged real image by the corresponding element lenses of the 1st lens array 2. The corresponding element lens of the 2nd lens array 3 is positioned at the enlarged real image formed position, and the front side focal plane 41 of the illumination lens 4 is positioned on a plane where the enlarged real image is formed, and a plane including the illuminated area is positioned on the rear side focal plane 42 of the illumination lens 4.