CUTTING TOOL

A cutting tool includes: a tool main body; a tube-shaped portion formed on a distal end portion of the tool main body; a hole machining tool core detachably fitted to an inside of the tube-shaped portion; and a head portion having a plurality of cutting edges and which is fitted to an outside of the tube-shaped portion. A circumferential wall of the tube-shaped portion includes an outer wall portion, an inner wall portion, and a fluid chamber which is formed in the circumferential wall between the outer and inner wall portions, wherein a fluid being filled in the fluid chamber. While increasing a pressure of the fluid in the fluid chamber, the outer wall portion is elastically deformed outward and thereby being pressed to the head portion, and the inner wall portion is elastically deformed inward and thereby being pressed to the hole machining tool core.