An optical plate is an optical plate for irradiating a target with light, and includes a light input surface for inputting the light, a light output surface for outputting the light, a back surface opposite to the light output surface, and a light diffusion portion formed at least inside the optical plate by converging laser light, for diffusing the light. The light input surface is a surface between the light output surface and the back surface, and the light input from the light input surface is diffused in the light diffusion portion and output from the light output surface.