An illumination device comprising: an optical element including a hologram recording medium which is configured to: diffract first coherent light beams having a first wavelength range so as to reproduce first images of a scattering plate; and diffract second coherent light beams having a second wavelength range which is different from the first wavelength range so as to reproduce second images of the scattering plate; and an irradiation device configured to irradiate the optical element with light beams having different wavelength ranges so as to allow the first coherent light beams and the second coherent light beams to scan the hologram recording medium, wherein the optical element includes a first hologram element and a second hologram element, the first and second hologram elements (55a, 55b) being arranged side by side on one plane so as to constitute the hologram recording medium, wherein the first hologram element is provided corresponding to the first coherent light beams having the first wavelength range and is configured to diffract the first coherent light beams so as to reproduce the first images of the scattering plate, wherein the second hologram element is provided corresponding to the second coherent light beams having the second wavelength range and is configured to diffract the second coherent light beams so as to reproduce the second images of the scattering plate, and wherein the irradiation device and the optical element are arranged such that: the first coherent light beams incident from the irradiation device on respective positions of the hologram recording medium are diffracted by the hologram recording medium and reproduce the first images of the scattering plate superimposed on a zone; and the second coherent light beams incident from the irradiation device on respective positions of the hologram recording medium are diffracted by the hologram recording medium and reproduce the second images of the scattering plate superimposed on the zone so as to illuminate the zone with reproduction light beams which reproduce the first and second images of the scattering plate. an optical element including a hologram recording medium which is configured to: diffract first coherent light beams having a first wavelength range so as to reproduce first images of a scattering plate; and diffract second coherent light beams having a second wavelength range which is different from the first wavelength range so as to reproduce second images of the scattering plate; and diffract first coherent light beams having a first wavelength range so as to reproduce first images of a scattering plate; and diffract second coherent light beams having a second wavelength range which is different from the first wavelength range so as to reproduce second images of the scattering plate; and an irradiation device configured to irradiate the optical element with light beams having different wavelength ranges so as to allow the first coherent light beams and the second coherent light beams to scan the hologram recording medium, wherein the optical element includes a first hologram element and a second hologram element, the first and second hologram elements (55a, 55b) being arranged side by side on one plane so as to constitute the hologram recording medium, wherein the first hologram element is provided corresponding to the first coherent light beams having the first wavelength range and is configured to diffract the first coherent light beams so as to reproduce the first images of the scattering plate, wherein the second hologram element is provided corresponding to the second coherent light beams having the second wavelength range and is configured to diffract the second coherent light beams so as to reproduce the second images of the scattering plate, and wherein the irradiation device and the optical element are arranged such that: the first coherent light beams incident from the irradiation device on respective positions of the hologram recording medium are diffracted by the hologram recording medium and reproduce the first images of the scattering plate superimposed on a zone; and the second coherent light beams incident from the irradiation device on respective positions of the hologram recording medium are diffracted by the hologram recording medium and reproduce the second images of the scattering plate superimposed on the zone the first coherent light beams incident from the irradiation device on respective positions of the hologram recording medium are diffracted by the hologram recording medium and reproduce the first images of the scattering plate superimposed on a zone; and the second coherent light beams incident from the irradiation device on respective positions of the hologram recording medium are diffracted by the hologram recording medium and reproduce the second images of the scattering plate superimposed on the zone so as to illuminate the zone with reproduction light beams which reproduce the first and second images of the scattering plate.