Insert for the cutting tool according to the present invention is used is bonded to the cutting tool holder for, has the same polygon onto another side first side and a second is arranged to face the opposite sides in the thickness direction, and the first face second 2 has an insert body having a third surface which is disposed along the first surface and the rim of the second face between the surface, the first surface and the third sides edges, at least one edge portion of the parts formed by the blood in for the cutting tool insert having cutting parts of the day for cutting the sakmul, cracks generated on the cutting blade by the chipping when the chipping occurs in the cutting blade to the cutting when the machinability of water by said cutting blade that prevents the radio portion corner formed above by the second surface and the third surface, the third surface of forming the cutting edge portion is formed edge with the first surface, the crack propagation is formed is recessed about the third surface It characterized in that the recess is in preventing provided. In this way, even if chipping occurs during cutting, since the cracks caused by the chipping do not propagate to the other cutting blade formed on the other side, for the cutting tool holder which is equipped with an insert for the life and the cutting tool for the cutting tool insert this life is to be increased.