A plate-like grid (24) where beam passage holes (26) are formed and a plate-like forming die (36a) are provided. The forming die has spacer forming holes (40a) and has hole forming portions (56a) that are located around the individual spacer forming holes so as to define the spacer forming holes and are formed of an ultraviolet ray transmission material. The forming die is brought into close contact with a surface of the grid to form an assemble body comprising the forming die and the grid. Either before or after the assemble body is formed, a spacer forming material (46) with ultraviolet curing characteristics is filled in each of the spacer forming holes of the forming die. Ultraviolet rays are irradiated, directly or by transmitting them through the hole forming portions, to the spacer forming material in order to cure the space forming material. After that, the forming die is separated from the grid with the cured spacer forming material left on the grid.