A device for producing a master diffraction grating includes a light source unit and a reflecting member 11. The light source unit forms a first interference fringe by irradiating a substrate surface of a master substrate 101 with light. The reflecting member 11 reflects the light from the light source unit reflected on the substrate surface of the master substrate 101 and guides the light again to the substrate surface side to form a second interference fringe. A resist pattern based on the first interference fringe and the second interference fringe is formed on the substrate surface of the master substrate 101.