An illumination device has an optical device and an irradiation unit. The irradiation unit has a light source emitting a coherent light beam, and a scanning device capable of adjusting a reflection angle of the coherent light beam emitted from the light source. The light source has light sources emitting a plurality of coherent light beams having an identical wavelength range, the hologram recording medium has a recording area to be scanned with each of a plurality of coherent light beams reflected by the scanning device, and the recording area has an interference fringe that diffracts an incident coherent light beam. The optical device uses the plurality of coherent light beams diffracted by the interference fringe of the recording area so that each of the coherent light beams diffracted by the hologram recording medium is superimposed on at least one portion to reproduce the image of the reference member.