A plurality of through holes having an equal size are formed in an underlay substrate. Positions of the plurality of through holes are suitably set according to the shape of a substrate sheet. Specifically, an equal number of through holes are formed in each of end blank corresponding regions that, when the substrate sheet and the underlay substrate are overlapped with each other, overlap with end blank regions of the substrate sheet, of the underlay substrate. In addition, the through holes are formed at equal spacing in portions excluding the end blank corresponding regions in a blank corresponding region, which overlaps with a blank region of the substrate sheet, of the underlay substrate.