PURPOSE: To solve the problem that the tool changing times are numerous and the production efficiency is low because of a work being moved in one directional positioning movement method in the case of executing drilling on the work with the tool installed to the drilling machine equipped with a tool changing device.

CONSTITUTION: In the case of machining the different diameter holes in many kinds on the web face of a shape steel W as for a work with drills 35A, 35B, 35C as for a tool via spindle 33A, 33B, 33C of the upper drill head 31 of the shape steel dirlling machine 1 equipped with a tool support device 39 which is a tool change device, the different diameter holes in many kinds executing drilling on the shape steel W in advance are subjected to grouping in plural sets on each of the same diameter. The two directional positioning movement method of the shape steel W of the X axial direction advance and retreat is employed. The changing times of the drill 35C can be reduced more than the past by taking the method executing the drilling of the 2nd group at the retreat time of the 1st group at the advance time.