PURPOSE: To drill a standard hole on a printed board in a highly accurate manner, by forming a hole mark, showing a reference hole drilling position, in a proper spot on an internal layer circuit board, and shifting the reference hole to a central position of the hole mark by a picture processing device.

CONSTITUTION: Part of an upper spot facing hole 12c of a plate 7, whose spot facing from both sides of a multilayer printed board 7 is finished, is moved to a lower part of an industrial television camera 21. Next, light is illuminated from the lower slant of this hole 12c by optical fibers 20 and 20, and the light transmitted image appearing in this hole 12c is photographed by the ITV camera 21, then this image is subjected to a picture process by a picture processor 29. With this constitution, a center point of a hole mark is directly taken out, thus a reference hole's drilling position is detected in a highly accurate manner without entailing any errors.