To perform drilling working and/or cutting working for a plastic substrate by punch working so that burr may not be left in a punching edge part.

Drilling working of many slits 12 is performed by punch working of two times in a worksheet 11 of a plastic substrate. In the first punch working, original form slits 17 which are slightly smaller than the sizes of required slits 12 are punched. Subsequently, punch working is performed so as to cut the internal edge parts of the original form slits 17 by small amount α and finish working to slits 12 of required sizes (W+2α) is performed for the original form slits 17, in the second punch working. As a result, burr 18 produced in the first punch working is cut and the slits 12 without burr 18 are formed. Subsequently, working in which the worksheet 11 is cut into a tape-shape is performed by working of two times in the same way and a tape shape 24 without burr 26 is formed in a punching edge part.