To achieve a method of forming a screw thread hole for efficiently stably obtaining a structure capable of securing strength of a screw.

A chamfer part 33 is formed at an opening on a broken section side of a lower hole 14a formed at a part of a material 13a by punching. At this time, a rod part 29 of a coining punch 26 is inserted into the lower hole 14a without a gap and a step part 30 presses a surrounding part around a part for forming the chamfer part 33. A blank is moved to a broken section part by the formation of the chamfer part 33 and the diameter of the broken section part is reduced to allow the lower hole 14a to have an almost uniform cylindrical surface. In this state, when the screw is formed at the lower hole 14a, the rise of the thread of the screw at the broken section part is secured so that the strength of the screw is secured.