A cutting insert, wherein: a cutting edge is formed on a peripheral border of a rake face of an insert body, the cutting edge having a corner portion and a pair of inclined portions adjoining to the both ends of the corner portion, respectively; a protruding section is formed close to the rake face so as to protrude at a distance away from the cutting edge; a pair of convex sections is formed on both sides of a bisector, dividing the corner portion, in the range from a wall surface of the protruding section to the rake face, so as to extend toward the cutting edge; the convex sections face toward the corner portion of the cutting edge; the convex sections include first wall surfaces that are more separated from each other to extend toward both ends of the corner portion, respectively, as the first wall surfaces are farther from the wall surface of the protruding section and closer to the cutting edge, and second wall surfaces that extend toward the cutting edge adjoined to the both ends of the corner portion by intersecting with the first wall surfaces; the first wall surfaces and the second wall surfaces are inclined surfaces that are inclined with respect to the rake face and that intersect with each other to form intersection ridgelines; the intersection ridgelines intersect with the wall surface of the protruding section in a corner portion side of the protruding section and at a position lower than a top portion of the protruding section; characterized in that a tilt angle (γ) of the second wall surfaces in a cross section orthogonal, in a top view of the cutting insert, to the inclined portion adjoined to the both ends of the corner portion is smaller than a tilt angle (α) of the first wall surfaces in the cross section orthogonal, in a top view of the cutting insert, to the intersection ridgelines; and a tilt angle (β) of the second wall surfaces in the cross-section orthogonal, in a top view of the cutting insert, to the intersection ridgelines is smaller than the tilt angle (α) of the first wall surfaces in the cross-section orthogonal, in a top view of the cutting insert, to the intersection ridgelines. a cutting edge is formed on a peripheral border of a rake face of an insert body, the cutting edge having a corner portion and a pair of inclined portions adjoining to the both ends of the corner portion, respectively; a protruding section is formed close to the rake face so as to protrude at a distance away from the cutting edge; a pair of convex sections is formed on both sides of a bisector, dividing the corner portion, in the range from a wall surface of the protruding section to the rake face, so as to extend toward the cutting edge; the convex sections face toward the corner portion of the cutting edge; the convex sections include first wall surfaces that are more separated from each other to extend toward both ends of the corner portion, respectively, as the first wall surfaces are farther from the wall surface of the protruding section and closer to the cutting edge, and second wall surfaces that extend toward the cutting edge adjoined to the both ends of the corner portion by intersecting with the first wall surfaces; the first wall surfaces and the second wall surfaces are inclined surfaces that are inclined with respect to the rake face and that intersect with each other to form intersection ridgelines; the intersection ridgelines intersect with the wall surface of the protruding section in a corner portion side of the protruding section and at a position lower than a top portion of the protruding section; characterized in that a tilt angle (γ) of the second wall surfaces in a cross section orthogonal, in a top view of the cutting insert, to the inclined portion adjoined to the both ends of the corner portion is smaller than a tilt angle (α) of the first wall surfaces in the cross section orthogonal, in a top view of the cutting insert, to the intersection ridgelines; and a tilt angle (β) of the second wall surfaces in the cross-section orthogonal, in a top view of the cutting insert, to the intersection ridgelines is smaller than the tilt angle (α) of the first wall surfaces in the cross-section orthogonal, in a top view of the cutting insert, to the intersection ridgelines.