PURPOSE: To efficiently perform drilling work while ensuring high positioning accuracy, by mounting a workpiece supported on a V block with an end face butt mating to a reference pin, and further moving with a vernier of a measuring device an inserting bush to an assigned drilling spot.

CONSTITUTION: A workpiece 8 of round material is mounted on a V groove of a V block 3, further after a workpiece end face is pressed so as to butt mate with a reference pin 5 implanted in a right end part of the V block 3, the workpiece 8 is lightly fixed so as to be pressed in from upward by a tightening screw 3b of a workpiece tightening tool 3a. Successively, a vernier 2b of a measuring device 2 is slide operated along a main scale 2a while making it coincide with an assigned drilling work position. In this way, the center of an inserting bush 6 mounted on a work positioning guide 4 is positioned in the assigned drilling work position. In this condition, a drill 9 is inserted to the inserting bush 6 from upward, to drill work the workpiece 8.