An illumination device including a light source; a light scanner for changing a light path of light-source light; a light diffusion device having element diffusion devices; and a light-path adjustment device disposed on a light path of the light-source light, the light-path adjustment device having element adjustment devices corresponding to respective element diffusion devices, adjusting a light path of the light-source light. 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 on the element diffusion device. Each element diffusion device illuminates an element illumination area corresponding to the element diffusion device.