An illumination device comprising: a diffusing element comprising concave unit lenses or convex unit lenses an irradiation device including a light source device configured to emit coherent light and a scanning device configured to direct the traveling direction of the coherent light from the light source device in such a manner that it scans the light on the diffusing element; a first lens array, facing the diffusing element, for changing a path of coherent light that has been diffused by the diffusing element; a second lens array, facing the first lens array, for changing a path of light whose light path has been changed by the first lens array; and a deflecting element, facing the second lens array, configured to change a path of light whose light path has been changed by the second lens array, wherein a first and second diffused lights are configured to travel to illuminated regions which at least partly overlap each other after the paths of the first and second diffused lights are respectively controlled by the first lens array, the second lens array and the deflecting element, the first diffused light having entered a first region on the diffusing element and having been diffused by the diffusing element, and the second diffused light having entered a second region of the diffusing element which differs from the first region, on the diffusing element and having been diffused by the diffusing element, wherein the first lens array includes first unit lenses, and the second lens array includes second unit lenses each corresponding to each first unit lens, and characterized in that in a plane parallel to an optical axis of a first unit lens and crossing the first unit lens along a maximum width, a diffusion angle of diffused light exiting the diffusing element is equal to or less than an angle formed between two line segments extending from a principal point of a second unit lens, facing the first unit lens, to both ends of the first unit lens along its maximum width. a diffusing element comprising concave unit lenses or convex unit lenses an irradiation device including a light source device configured to emit coherent light and a scanning device configured to direct the traveling direction of the coherent light from the light source device in such a manner that it scans the light on the diffusing element; a first lens array, facing the diffusing element, for changing a path of coherent light that has been diffused by the diffusing element; a second lens array, facing the first lens array, for changing a path of light whose light path has been changed by the first lens array; and a deflecting element, facing the second lens array, configured to change a path of light whose light path has been changed by the second lens array, wherein a first and second diffused lights are configured to travel to illuminated regions which at least partly overlap each other after the paths of the first and second diffused lights are respectively controlled by the first lens array, the second lens array and the deflecting element, the first diffused light having entered a first region on the diffusing element and having been diffused by the diffusing element, and the second diffused light having entered a second region of the diffusing element which differs from the first region, on the diffusing element and having been diffused by the diffusing element, wherein the first lens array includes first unit lenses, and the second lens array includes second unit lenses each corresponding to each first unit lens, and characterized in that in a plane parallel to an optical axis of a first unit lens and crossing the first unit lens along a maximum width, a diffusion angle of diffused light exiting the diffusing element is equal to or less than an angle formed between two line segments extending from a principal point of a second unit lens, facing the first unit lens, to both ends of the first unit lens along its maximum width.