An illumination device includes a diffusion member having an anisotropic diffusion surface, a rotary shaft member configured to rotate the anisotropic diffusion surface while a coherent light beam from a light source is illuminated on the anisotropic diffusion surface, and an optical device that further diffuses a coherent light beam diffused on the anisotropic diffusion surface, wherein the coherent light beam diffused on the anisotropic diffusion surface is diffused in a form of line and the diffused coherent light beam in the form of line is configured to move to draw a locus of rotation in one direction in accordance with the rotation of the anisotropic diffusion surface.