There is provided a method for manufacturing a diffractive optical element that can suppress the generation of heat from the inside of an insulative substrate and stabilize an etching rate. A method for manufacturing a diffractive optical element composed of an insulative substrate whose surface has a bumpy structure includes a selecting step of selecting an insulative substrate having an electrical resistivity equal to or higher than a certain value by measuring electrical resistivity of insulative substrates; and an etching step of forming a bumpy structure by dry etching in a surface of the insulative substrate selected in the selecting step.