| 摘要 |
PROBLEM TO BE SOLVED: To enhance the utilizing efficiency of the light of an illumination optical system and to make easily manufacturable a lens array used for a splitting optical system. SOLUTION: This illumination optical system is provided with a light source, the splitting optical system and a superimposing optical system. The splitting optical system is provided with a 1st lens array having plural small lenses splitting the light emitted from the light source into plural partial light fluxes and a 2nd lens array having plural small lenses corresponding to the plural small lenses of the 1st lens array respectively. The 2nd lens array is arranged near a position where the plural partial light fluxes emitted from the 1st lens array are condensed. Besides, plane surface parts are formed between plural lens columns constituted of the plural small lenses respectively. The plural small lenses of the 2nd lens array are formed to be polygonal other than almost rectangular according to the contour shape of the partial light fluxes condensed by the plural corresponding small lenses of the 1st lens array.
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