A cutting tool including an insert and a holder to which the insert is secured. The insert has a rod with a substantially circular transverse cross-section. The insert includes a shank portion and a cutting edge portion. The cutting edge portion is located at an end portion continuous with the shank portion. In the cutting edge portion, one end of a cutting edge ridge protrudes toward the periphery of the rod. When the insert is secured to the holder, the cutting edge ridge has a negative radial rake angle.