An illumination device illuminating an illumination area, comprising: a light source; a light scanner capable of changing a light path of light-source light emitted from the light source; a light diffusion device having element diffusion devices that diffuse the light-source light, wherein the respective element diffusion devices are formed of element holograms storing interference fringe patterns different from one another; and a light-path adjustment device disposed on a light path of the light-source light from the light scanner up to the light diffusion device, the light-path adjustment device having element adjustment devices that are provided correspondingly to the respective element diffusion devices, and adjust a light path of the light-source light toward the corresponding element diffusion devices, wherein the light-path adjustment device has a lens array including unit lenses constituting the element adjustment devices; wherein: an incident position of the light-source light on the light-path adjustment device varies depending on a light path determined by the light scanner; an incident angle of the light-source light on each element diffusion device varies depending on an incident position on the element adjustment device corresponding to the element diffusion device; an emergent angle from each element diffusion device varies depending on the incident angle; each element diffusion device illuminates an element illumination area (Zp) corresponding to the element diffusion device; the element diffusion devices and the element adjustment devices are arranged along one direction; and the illumination area is divided into element illumination areas (Zp), which are arranged in a lattice pattern, wherein element illumination areas (Zp) corresponding to the respective element diffusion devices are not overlapped with one another. a light source; a light scanner capable of changing a light path of light-source light emitted from the light source; a light diffusion device having element diffusion devices that diffuse the light-source light, wherein the respective element diffusion devices are formed of element holograms storing interference fringe patterns different from one another; and a light-path adjustment device disposed on a light path of the light-source light from the light scanner up to the light diffusion device, the light-path adjustment device having element adjustment devices that are provided correspondingly to the respective element diffusion devices, and adjust a light path of the light-source light toward the corresponding element diffusion devices, wherein the light-path adjustment device has a lens array including unit lenses constituting the element adjustment devices; wherein: an incident position of the light-source light on the light-path adjustment device varies depending on a light path determined by the light scanner; an incident angle of the light-source light on each element diffusion device varies depending on an incident position on the element adjustment device corresponding to the element diffusion device; an emergent angle from each element diffusion device varies depending on the incident angle; each element diffusion device illuminates an element illumination area (Zp) corresponding to the element diffusion device; the element diffusion devices and the element adjustment devices are arranged along one direction; and the illumination area is divided into element illumination areas (Zp), which are arranged in a lattice pattern, wherein element illumination areas (Zp) corresponding to the respective element diffusion devices are not overlapped with one another. an incident position of the light-source light on the light-path adjustment device varies depending on a light path determined by the light scanner; an incident angle of the light-source light on each element diffusion device varies depending on an incident position on the element adjustment device corresponding to the element diffusion device; an emergent angle from each element diffusion device varies depending on the incident angle; each element diffusion device illuminates an element illumination area (Zp) corresponding to the element diffusion device; the element diffusion devices and the element adjustment devices are arranged along one direction; and the illumination area is divided into element illumination areas (Zp), which are arranged in a lattice pattern, wherein element illumination areas (Zp) corresponding to the respective element diffusion devices are not overlapped with one another.