An optical element is provided. When in a xz cross section, an angle which a ray travelling from the origin at θr forms with the normal to the light receiving surface is designated as φx, an angle which a ray travelling from b in the z axis direction forms, after the surface, with the z axis direction is designated as θib, in a yz cross section, an angle which a ray travelling from the origin at θr forms with the normal to the light receiving surface is designated as φy, angles which a ray travelling from a in the z axis direction forms, after the light receiving and exiting surfaces, with the z axis direction are designated as θia and θea, and an angle which a ray travelling from the origin at arctan(a/ha) forms, after the light exiting surface, with the z axis direction is designated as θeha, φy>φx (0 45° θea>45° θia>θib are satisfied.