PURPOSE: To increase speed of drilling work and to secure necessary and sufficient drilling precision.

CONSTITUTION: A standard mark 1a is provided on a multilayer printed board 1, an image of this mark 1a is picked up by an X ray camera 2, a binarized image data for an observation screen previously specified by an image processing circuit 4 is outputted and it is regenerated by a monitor TV 5. A central coordinate of the mark 1a is detected by a mark center computing circuit 6 in accordance with the image data from the image processing circuit 4. The observation screen is divided into a plural number of small ranges, and correction data to correspond with the small ranges are memorized in a correction data memory circuit 7. A calibrated central coordinate of the mark is output by a control circuit 8 in accordance with the central coordinate of the mark output from the mark center computing circuit 6 and the correction data of the small ranges where this central coordinate is positioned. An XY table device 10 is moved by this output, a position of a drill 11 is made to match the calibrated central coordinate, and drilling is carried out.