To shorten the time required for adjustment work in a site by easily performing the rotation adjustment work for an adjust screw for adjusting the position in the axial direction of a tool of a tip.

A throwaway tip 5 is removably mounted on a tip mounting seat 3 formed in the outer periphery of the tip part of a substantially disc-like tool main body 1 rotated round an axis O with its seated surface closely adhering thereto. The adjust screw 9 is screw-engaged with a female screw part 7b formed in the wall surface 3c of the tool base end side of the tip mounting seat, and by rotating the adjust screw 9, the throwaway tip 5 is adjusted to the position in the direction of the tool axis through a pressing pin 8. In rotating the adjust screw 9, the tool is inserted from a tool base end opening of a through hole 7 penetrating a shoulder part 1b of the tool main body, and the tip of the tool is engaged with the engagement part of the head of the adjust screw to rotate the screw. Thus, the adjust screw can be freely rotated.