An illumination device includes: a light source section having plural kinds of light sources, in which the light sources emits light beams having different wavelengths; a parallelizing optical system parallelizing each of the light beams entered from the light sources, and allowing each of the parallelized light beams to exit therefrom; a light path unifying optical system unifying the parallelized light beams exited from the parallelizing optical system into a single light path; an expanding optical system expanding a beam diameter of each of the parallelized light beams unified into the single light path, and allowing each of the expanded and parallelized light beams to exit therefrom; and a uniformizing optical system uniformizing an in-plane intensity distribution in each of the expanded and parallelized light beams exited from the expanding optical system.