PURPOSE: To perform accurate and automatic positioning when the position of a drill is matched with a prepared hole to effect cutting after the prepared hole is formed in a work.

CONSTITUTION: A prepared hole is formed in the surface of a work by using a drill for premachining having length lower than the depth of the hole to be machined and reduced in resilient deformation (at a step 100). The drill is exchanged into a drill for machining having length higher than the depth (at a step 101) and the work is cut (at a step 102). The component of force, within a surface crossing the axial direction of the drill at right angles, of components of force exerted on the drill when the tip of the drill is brought into contact with the vicinity of the prepared hole of the work is detected (at a step 103). The tip position of the drill is moved in a direction in which the component of force is reduced (at a step 104).