To form a hole for electrically connecting an upper conductor layer 11 of an insulating layer 10 of a printed wiring board 1 and a lower conductor layer 12 of the insulating layer 10 in the insulating layer 10 to expose the lower conductor layer 12 to the hole bottom, when laser processing is executed for making the hole 13 in the insulating layer 10 using the printed wiring board 1 comprising a treatment layer 14 being placed between the lower conductor layer 12 and the insulating layer 10 for emitting an electromagnetic wave having a wavelength different from the wavelength of processing laser during the laser processing, change in a signal emitted from the treatment layer 14 of the printed wiring board 1 is measured to determine the remaining state of the insulating layer 10. The electromagnetic wave emitted in laser processing from the treatment layer 14 placed between the lower conductor layer 12 and the insulating layer 10 rather than the reflection of laser of laser is used, so that the hole 13 piercing the insulating layer can be detected precisely.