Provided is an optical element capable of reducing Fresnel (surface) reflection on a lens surface which causes flare or ghost, an optical system including the optical element, and an optical scanning device including the optical element. The optical element includes: a plurality of two-dimensionally arranged subwave structures having an anti-reflection function, and in the optical element when directions orthogonal to each other within a plane including a tangent of a vertex of the optical surface are set as a first and second directions, each of distances between the subwave structures changes in at least one of the first and second directions, and an arbitrary subwave structure is located with a state in which a distance between the arbitrary subwave structure and one of the subwave structures closest to the arbitrary subwave structure is shorter than 1/2 of an average wavelength of the light beam incident on the optical surface.