A superhard sintered body (1) containing cubic boron nitride is bonded to an apical angle part (5) of a tool body (2) having a polygonal shape, and an edge and a chip breaker are formed on the superhard sintered body (1). A chamfer is formed on the intersection between the upper surface and the side surface of the superhard sintered body (1), the chip breaker has a protrusion (6), and an angle θ formed by ridges (6b, 6c) on the apex of the protrusion (6) or a tangential line at a point bisecting the ridges (6b, 6c) and a bisector (9a) for the apical angle and the ratio of the distance (L1) between a first intersection (P) between the two ridges (6b, 6c) on the apex of the protrusion (6) and an extreme point (S) of the first ridge (6b) to the distance (L2) between a second intersection (Q) between a straight line passing through the first intersection (L1) and the extreme point (S) and the outer periphery of the tool body (2) and the first intersection (Q) are in prescribed ranges.