An illumination optical system is provided that is configured to guide light emitted from a light source to an image generation unit that is arranged to be movable in a direction perpendicular to incoming light and is configured to generate an image by reflecting the incoming light. The illumination optical system includes a first lens that is arranged to be movable in a direction perpendicular to an optical axis of the first lens, a second lens that is arranged to be movable in a direction that changes a face-to-face distance between the first lens and the second lens, and a lens position control unit configured to displace the first lens and the second lens.