To inexpensively and easily produce a distributed density mask at a high production speed without requiring a special equipment.

A mask blank is divided into unit cells and light transmissive regions or light shielding regions of the respective unit cells are determined. The determined blight transmissive regions or light shielding regions are disposed on each grid and necessary pattern forming energy, focal depth and beam diameter are calculated every grid by CAD(computer aided design) and converted to data. The sensitive material of the mask blank is patterned on the basis of the data under prescribed conditions (focal depth and beam diameter) and the mask blank is developed and rinsed to obtain a three-dimensional sensitive material pattern. The shape of the sensitive material pattern is transferred to a light shielding film by etching.