To easily form diaphragms with a narrower width and at narrower pitches in order to provide a finer image.

In this method, an insulating layer 11 made of a thermally curable insulating material for diaphragm formation is formed on a substrate 2 which composes a display panel and on which diaphragms are to be formed. Then, laser beam 12 is radiated to the surface of the insulating layer 11 to thermally cure only the parts to become diaphragms and carry out patterning of the diaphragms. After that, a sand blast treatment is carried out for the patterned insulating layer 11 to remove non-cured parts 11-2 and diaphragms 2b are formed from the remaining thermally cured parts 11-1.