An illumination optical system including one or more light sources each including a solid-state light-emitting device and an optical member. The optical member includes an integrator including a first fly-eye lens on which light from the solid-state light-emitting device is incident and a second fly-eye lens on which light from the first fly-eye lens is incident, and uniformizing a luminance distribution of light in a predetermined illumination region illuminated with light incident from the solid-state light-emitting device. A major-axis direction of a luminance distribution shape of light incident on an incident plane of the first fly-eye lens is different from arrangement directions of the cells in the first fly-eye lens.
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