An illumination device comprising: an optical device including a hologram recording medium capable of reproducing an image of a reference member on an illumination zone, the optical device varying an incidence angle of a coherent light beam at each position on the illumination zone, and an irradiation unit configured to irradiate a coherent light beam to the optical device so that the coherent light beam scans the hologram recording medium, wherein the irradiation unit comprises: a light source for emitting a coherent light beam; and a scanning device configured to be capable of adjusting a reflection angle of the coherent light beam emitted from the light source and to make a reflected coherent light beam scan on the hologram recording medium, wherein the light source comprises a plurality of light sources (61r, 61g, 61b) for emitting a plurality of coherent light beams having different wavelength ranges, the hologram recording medium comprises a plurality of recording areas (55r, 55g, 55b) to each be scanned with a coherent light beam reflected by the scanning device, respectively, each of the plurality of recording areas (55r, 55g, 55b) comprises an interference fringe that diffracts the coherent light beam of the corresponding wavelength range, the scanning device is configured to make each coherent light beam of a specific wavelength incident on specific positions in the respective recording area (55r, 55g, 55b) on the hologram recording medium at an incident angle that meets the Bragg condition on the respective positions, and the coherent light beams incident on the specific positions in the respective recording areas (55r, 55g, 55b) reproduce images of the reference member in a manner that the images are superimposed one another on an entire region of the illumination zone by diffraction caused by interference fringes recorded in the hologram recording medium. an optical device including a hologram recording medium capable of reproducing an image of a reference member on an illumination zone, the optical device varying an incidence angle of a coherent light beam at each position on the illumination zone, and an irradiation unit configured to irradiate a coherent light beam to the optical device so that the coherent light beam scans the hologram recording medium, wherein the irradiation unit comprises: a light source for emitting a coherent light beam; and a scanning device configured to be capable of adjusting a reflection angle of the coherent light beam emitted from the light source and to make a reflected coherent light beam scan on the hologram recording medium, wherein the light source comprises a plurality of light sources (61r, 61g, 61b) for emitting a plurality of coherent light beams having different wavelength ranges, the hologram recording medium comprises a plurality of recording areas (55r, 55g, 55b) to each be scanned with a coherent light beam reflected by the scanning device, respectively, each of the plurality of recording areas (55r, 55g, 55b) comprises an interference fringe that diffracts the coherent light beam of the corresponding wavelength range, the scanning device is configured to make each coherent light beam of a specific wavelength incident on specific positions in the respective recording area (55r, 55g, 55b) on the hologram recording medium at an incident angle that meets the Bragg condition on the respective positions, and the coherent light beams incident on the specific positions in the respective recording areas (55r, 55g, 55b) reproduce images of the reference member in a manner that the images are superimposed one another on an entire region of the illumination zone by diffraction caused by interference fringes recorded in the hologram recording medium. a light source for emitting a coherent light beam; and a scanning device configured to be capable of adjusting a reflection angle of the coherent light beam emitted from the light source and to make a reflected coherent light beam scan on the hologram recording medium, wherein the light source comprises a plurality of light sources (61r, 61g, 61b) for emitting a plurality of coherent light beams having different wavelength ranges, the hologram recording medium comprises a plurality of recording areas (55r, 55g, 55b) to each be scanned with a coherent light beam reflected by the scanning device, respectively, each of the plurality of recording areas (55r, 55g, 55b) comprises an interference fringe that diffracts the coherent light beam of the corresponding wavelength range, the scanning device is configured to make each coherent light beam of a specific wavelength incident on specific positions in the respective recording area (55r, 55g, 55b) on the hologram recording medium at an incident angle that meets the Bragg condition on the respective positions, and the coherent light beams incident on the specific positions in the respective recording areas (55r, 55g, 55b) reproduce images of the reference member in a manner that the images are superimposed one another on an entire region of the illumination zone by diffraction caused by interference fringes recorded in the hologram recording medium.