To provide a diffraction optical element capable of obtaining high optical performance even though the formation density of a recessed and projecting pattern is non-uniform.

In the diffraction optical device 10 having a diffraction surface 10c where the recessed and projecting pattern is formed with non-uniform density, the surface roughness of the smooth part of the recessed and projecting pattern is made smaller according as it is the recessed and projecting pattern 10c-1 having the lower formation density. It is realized by selectively using two or more kinds of cutting tools having different edge diameters in accordance with the formation density of the recessed and projecting pattern when performing the cutting work of the original die of the diffraction optical device or the metallic die for molding the diffraction optical device.