Cutting tool

A cutting tool extending along a center axis, and including on a front end side a cutting insert to cut a work material, the cutting tool comprising:

• a head portion which includes an insert mounting seat, on which the cutting insert is installed, on a front end side;
• a holder which is installed on a rear end side of the head portion and holds the head portion;
• a fixing member which fixes a position of the head portion with respect to the holder when the head portion is mounted on the holder;
• and
• a ring portion, wherein
• the head portion is configured to be mountable on the holder, with an angle thereof changing around the center axis,
• on one end face of the ring portion, a first engaging portion, which engages with the engaging portion of the head portion, is disposed, and on the other end face of the ring portion, a second engaging portion, which engages with the engaging portion of the holder, is disposed,
• the head portion is configured to be engageable with the ring portion, with an angle thereof changing around the center axis,
• the holder is configured to be engageable with the ring portion, with an angle thereof changing around the center axis,
• the unit of change of the engaging angle of the head portion with respect to the ring portion is different from the unit of change of the engaging angle of the holder with respect to the ring portion, and
• the cutting tool is configured to change a radial rake angle of the cutting insert installed on the head portion by changing the engagement angle of the head portion with respect to the ring portion and the engagement angle of the holder with respect to the ring portion.