PROBLEM TO BE SOLVED: To provide an illumination optical device and a projector in which uneven illuminance is less likely to occur. An illumination optical device includes a light source device and a homogenization device that emit light in a first direction along an illumination optical axis. The light source device has first to fourth emission sections that emit first to fourth color light, and the homogenizing device is arranged in the third direction in the second direction with respect to the illumination optical axis, and the first color light is incident. The first array set is arranged in the second direction in the direction opposite to the third direction and the second color light is incident, and the third array set is arranged in the third direction in the direction opposite to the second direction. It includes a third array set on which the light is incident, a fourth array set on which the fourth color light is incident, which is arranged in the direction opposite to the second direction and in the direction opposite to the third direction, and a superimposing lens. Each array set includes a pair of lens arrays, and at least one array set is located on the illumination optical axis such that the first region is located in the first direction with respect to the second region, which has a longer distance from the illumination optical axis. It is tilted with respect to the orthogonal virtual planes. [Selection diagram] FIG. 8
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