A cutting insert comprising an upper surface, a lower surface, and a side surface connecting the upper surface and the lower surface, wherein: an intersecting edge between the upper surface and the side surface is partially or entirely provided with a cutting edge; the cutting edge comprises a linear or curved first major cutting edge, a linear or curved second major cutting edge connected to the first major cutting edge, a substantially arc-like corner cutting edge connected to the first major cutting edge on an opposite side of the second major cutting edge, and a linear or curved flat cutting edge connected to the corner cutting edge on an opposite side of the first major cutting edge; an angle (θ) formed by the linear second major cutting edge or a chord formed by connecting both ends of the curved second major cutting edge, and the linear first major cutting edge or a chord formed by connecting both ends of the curved first major cutting edge, is an obtuse angle; an interior angle (α) formed by the flat cutting edge and the linear first major cutting edge or the chord of the curved first major cutting edge is larger than an interior angle (β) formed by the flat cutting edge and the linear second major cutting edge or the chord of the curved second major cutting edge; a land is provided adjacent to the first major cutting edge on the upper surface; and a width of the land increases toward the corner cutting edge, characterized in that the land is also provided adjacent to the second major cutting edge on the upper surface, a width of the land increases toward the corner cutting edge, and a rate of increase of the width of the land adjacent to the first major cutting edge is larger than a rate of increase of the width of the land adjacent to the second major cutting edge. an intersecting edge between the upper surface and the side surface is partially or entirely provided with a cutting edge; the cutting edge comprises a linear or curved first major cutting edge, a linear or curved second major cutting edge connected to the first major cutting edge, a substantially arc-like corner cutting edge connected to the first major cutting edge on an opposite side of the second major cutting edge, and a linear or curved flat cutting edge connected to the corner cutting edge on an opposite side of the first major cutting edge; an angle (θ) formed by the linear second major cutting edge or a chord formed by connecting both ends of the curved second major cutting edge, and the linear first major cutting edge or a chord formed by connecting both ends of the curved first major cutting edge, is an obtuse angle; an interior angle (α) formed by the flat cutting edge and the linear first major cutting edge or the chord of the curved first major cutting edge is larger than an interior angle (β) formed by the flat cutting edge and the linear second major cutting edge or the chord of the curved second major cutting edge; a land is provided adjacent to the first major cutting edge on the upper surface; and a width of the land increases toward the corner cutting edge, characterized in that the land is also provided adjacent to the second major cutting edge on the upper surface, a width of the land increases toward the corner cutting edge, and a rate of increase of the width of the land adjacent to the first major cutting edge is larger than a rate of increase of the width of the land adjacent to the second major cutting edge.