PURPOSE: To provide a photomask capable of low-cost production of various diffraction gratings different from each other in cross-sectional shape and to produce optical parts with the photomask.

CONSTITUTION: Groups each consisting of openings 1 and light shielding parts 2 alternately arranged at narrow intervals incapable of resolution at the time of exposure are arranged at intervals capable of resolution to obtain the objective photomask 3. The light transmissivity of the openings 1 is varied by varying the area ratio of the openings 1 to the light shielding parts 2. When this photomask 3 is used, optical parts such as a diffraction grating whose cross-sectional shape corresponds to a variation of the light transmissivity can be produced.