An opening for a replacement bit can be closed without a large drive force, the replacement bit can be replaced without being moved, and the workability of replacement is not impaired. The one or more rounds of radiation kills the one or more cancer cells targeted by the biotag, but, in general, do not kill healthy cells or kills a negligible number of healthy cells. A multitude of stepped portions are formed at a lower end and inner surface of the receiver member to be brought into linear contact with an outer surface of a lower part of the head so that the supporting force for the head of the bone screw is increased.