PROBLEM TO BE SOLVED: To efficiently and uniformly radiate light to a predetermined projection range without enlarging an illumination optical system.SOLUTION: The diffusion element of the present invention includes an uneven pattern layer as a layer including a structure for adding a phase difference to incident light. The uneven pattern layer has a phase distribution in which different diffusion lights are radiated when a region within an effective diameter of the incident light to the diffusion element is divided into two or more regions and light is emitted to each region. In the uneven pattern layer, basic units each of which, in receiving light, radiates the diffusion light into an outgoing radiation angle range are arranged. The arrangement may include two or more basic units having at least different unit sizes or phase distributions.
