To effectively prevent the development of a crack and a whitening phenomenon, and to reduce a generating quantity of white powder when boring a hole in a printed wiring board.

In performing boring work by sandwiching this printed wiring board 1 having a prescribed wiring pattern by an upper metal mold 10 and a lower metal mold 20, ribs 21 are serially formed in a width of not coming to the wiring pattern along the whole edge periphery of a boring part of the printed wiring board 1 on the inside surface side of the lower metal mold 20, and when sandwiching the printed wiring board 1 under prescribed pressure by the upper metal mold 10 and the lower metal mold 20, the ribs 21 are made to bite into an edge part of the boring part, and are put in a state of being compressed more than the original thickness, and the hole is bored in the printed wiring board 1.