Illumination device, projection device, and projection-type image display device

An illumination device comprising:

• an optical element including a hologram recording medium which records an image of a scattering plate and diffracts a first coherent light beam having a first wavelength range and a second coherent light beam having a second wavelength range which is different from the first wavelength range so as to reproduce the image 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 beam and the second coherent light beam to scan the hologram recording medium,
• 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 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 images of the scattering plate superimposed on the zone so as to illuminate the zone with reproduction light beams which reproduce the images of the scattering plate.