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; and diffract second coherent light beams having a second wavelength range which is different from the first wavelength range; 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 such that incident angles of the first and second coherent light beams incident on the hologram recording medium change with time, 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 as a computer generated 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 illuminate an illuminated zone, 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 illuminate the illuminated zone, 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 illuminate the same illuminated 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 illuminate the same illuminated zone. an optical element including a hologram recording medium which is configured to: diffract first coherent light beams having a first wavelength range; and diffract second coherent light beams having a second wavelength range which is different from the first wavelength range; and diffract first coherent light beams having a first wavelength range; and diffract second coherent light beams having a second wavelength range which is different from the first wavelength range; 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 such that incident angles of the first and second coherent light beams incident on the hologram recording medium change with time, 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 as a computer generated 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 illuminate an illuminated zone, 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 illuminate the illuminated zone, 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 illuminate the same illuminated 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 illuminate the same illuminated zone.