An indexable type cutting tool comprises a drill having a shank and a drill body which extends from the shank, the drill body being defined with body flutes, and being formed with an insert seat which has seat side surfaces and a seat bottom surface and body flank surfaces and body thinning surfaces; a drill insert fitted into the insert seat of the drill body, having cutting edges and an insert bottom surface which is brought into close contact with the seat bottom surface, formed with insert flutes and insert side surfaces which are brought into close contact with the seat side surfaces, and defined with a through-hole which passes through the insert side surfaces; and a fastening screw for fastening the drill insert fitted into the insert seat to the drill.