PURPOSE: To facilitate formation of the inexpensive diffraction grating forming molds having excellent reproducibility and durability in a large quantity by forming a replica by photosensitive resin from one piece of a diffraction grating plate and etching the replica base and to obtain a photoresist having good adhesion without pinholes according to the method and device for applying the photoresist.

CONSTITUTION: This process for production of the diffraction grating forming molds includes a stage for forming the diffraction gratings 2 by ion beam etching on a quartz plate 1, a stage for forming the replica on another quartz plate 5 by the photosensitive resin 4 and, a stage for forming a release film 7 of Cr on the surface of the replica and a stage for forming the duplicated molds by forming the replica on a base 6 by the photosensitive resin 8 and subjecting this replica to ion beam etching. This method applies the photoresist on the quartz plate 1 by impressing ultrasonic vibrations to the photoresist and this coating device is used in the case of forming the diffraction gratings 2 consisting of the photoresist on the above-mentioned quartz plate.