Since the chip-breaking groove 30 is cut in the inner peripheral surface of the prepared hole 22 by compressing the chip-breaking tool 10 into the prepared hole 22 prior to the tapping process (the cutting process of the female thread) by the cut tap, the chip can be securely broken by the chip-breaking groove 30 and well discharged even in the case that the work 20 is made of the material having the high ductility. Accordingly, for example, as shown in FIG. 10, it is possible to prevent a lot of long connected chips from entwining the tap, it is unnecessary to monitor the tapping work, and it is possible to achieve a complete automation (an unmanned work). Further, it is possible to inhibit the cut tap from being broken due to the pinching of the chip, and it is easy to execute a treatment such as a chip cleaning or the like.