PURPOSE: To make it possible to process a precisely-deepened hole in a substrate by adjusting the elevation of a spindle, with the spindle lowered to the lowest limit to detect the elevation of a tool tip for controlling a drive supply for a spindle elevation adjusting mechanism according to an operational value in the difference thereof from a set value.

CONSTITUTION: X, Y tables 1, 2 are moved to locate a drill 5 at a hole, in which the drill is inserted and passed, in a drill elevation detecting device 11, and a spindle 8 is lowered to the lowest limit to allow insertion of the tip of the drill 5 therein. A control device operates a difference between a detected value input from the detecting device 11 and a set value to feed a signal to a motor 18, which is rotated by times of turn in normal/reverse direction specified by the signal in order to rotate a screw shaft 17 via gears 21, 22 for providing lengthening and shortening the interval between a coupling 7 and the spindle 8. The spindle 8, whose elevation is adjusted, is raised to move the tables 1, 2 for positioning the drill 5 at the place where a hole is made, and it is lowered to process a bottomed hole.