To reduce a period from the pattern design until the completion of die components in a trimming die having punches and a die.

The method for manufacturing the component (die) of a trimming die has a process for forming trimming apertures arranged in a predetermined pattern, and is used in the trimming die for trimming an insulation substrate by combining the punches corresponding to the trimming apertures with the die. In the process for forming the trimming apertures, such a metallic plate is used that has prepared holes which have the diameter smaller than that of the apertures of the trimming die and are preliminarily formed before the process for forming the trimming apertures in a lattice shape (regularly) within a region including the region in which the trimming apertures are formed. The diameter of the prepared holes corresponding to the position of the apertures to be formed among these apertures is enlarged up to a predetermined diameter by this method.