A refractive index controlled diffractive optical element having a two-dimensional refractive index distribution to be written on a transparent material, wherein a first refractive index region with a refractive index n1 and width d1 is formed in a transparent material, and the ith refractive index region with a refractive index ni (assuming ni≠ni−1) and a width di is formed adjacent to the (i−1)th refractive index region and opposite to the (i −2)th refractive index region (at an arbitrary side of the (i−1)th refractive index region when i=2) where i is an integer within a range of 2≦i≦x. Accordingly, a diffractive optical element simultaneously having high diffraction efficiency to a particular order and thinness of the element itself can be obtained.