PURPOSE: To perform the accurate drilling without generation of smear in a product area by operating a numerical control device at the time that the number of drilling time of a drill arrives a predetermined number, and changing the drill with a new one after drilling the predetermined number of time in an inspection area of a printed board.

CONSTITUTION: An inspection area data processing device 11, in which the number of drilling time and drilling positions of an inspection area are memorized, is provided separately from a product area data processing device 7, and the number of drilling time and drilling positions of through holes of a product area are memorized in the processing device 7. Next, a numerical control device 8 is operated to perform the drilling at the predetermined number of time in the product area on the basis of a command from the processing device 7. After drilling in the product area at the predetermined number of time corresponding to a lifetime of a drill, an alarm of drill change is output from the control device 8 to perform the drilling at a predetermined position of the product area at the predetermined number of time. Thereafter, at the time of concluding the drilling in the product area, the drill is changed with a new one.