A cutting insert (2) having a tip bit. (5) and a tabular tip body (4) supporting the tip. The cutting insert (2) is used by being mounted to the body (1) of a cutting tool. Wherein, the tip body (4) has a plurality of elastic deformation sections (8) separated by a slit (6) which extends on a transverse line from a corner to an area near another corner. The elastic deformation sections are moved closer together and elastically deformed within a plane which includes the tip body 4 when being mounted to the tool body 1. And, the opposing faces of the elastic deformation sections (8) have engaging sections (10) for engaging the tip bit (5).