An illumination device illuminating an illuminated zone comprising: an optical element including a hologram recording medium including a first zone and a second zone; the hologram recording medium being configured to reproduce images of a scattering plate; an irradiation device configured to irradiate the optical element with a coherent light beam such that the coherent light beam is allowed to scan the first zone and the second zone of the hologram recording medium in that the incident position of the coherent light beam is continuously changed with time, and such that the coherent light beams incident on respective positions in the first zone of the hologram recording medium are diffracted by the hologram recording medium to reproduce the images of the scattering plate superimposed on the same illuminated zone, and the coherent light beams incident on respective positions in the second zone of the hologram recording medium are diffracted by the hologram recording medium to reproduce the images of the scattering plate superimposed on the same illuminated zone; and a polarization control unit provided on an optical path of the coherent light beams, the polarization control unit being configured to control polarization of the coherent light beams such that a coherent light beam incident on the first zone of the hologram recording medium to travel toward a designated illumination zone has a first polarization component and such that a coherent light beam incident on the second zone of the hologram recording medium to travel toward a designated illumination zone has a second polarization component different from the first polarization component. an optical element including a hologram recording medium including a first zone and a second zone; the hologram recording medium being configured to reproduce images of a scattering plate; an irradiation device configured to irradiate the optical element with a coherent light beam such that the coherent light beam is allowed to scan the first zone and the second zone of the hologram recording medium in that the incident position of the coherent light beam is continuously changed with time, and such that the coherent light beams incident on respective positions in the first zone of the hologram recording medium are diffracted by the hologram recording medium to reproduce the images of the scattering plate superimposed on the same illuminated zone, and the coherent light beams incident on respective positions in the second zone of the hologram recording medium are diffracted by the hologram recording medium to reproduce the images of the scattering plate superimposed on the same illuminated zone; and a polarization control unit provided on an optical path of the coherent light beams, the polarization control unit being configured to control polarization of the coherent light beams such that a coherent light beam incident on the first zone of the hologram recording medium to travel toward a designated illumination zone has a first polarization component and such that a coherent light beam incident on the second zone of the hologram recording medium to travel toward a designated illumination zone has a second polarization component different from the first polarization component.