A cutting insert comprising: a seating surface; an outer peripheral surface contiguous to the seating surface; and a top surface contiguous to the outer peripheral surface and located opposite to the seating surface with the outer peripheral surface posed therebetween; the top surface having an external shape in a form of a polygon in a top view in which the top surface is viewed in a direction perpendicular to the seating surface and extending from the top surface toward the seating surface, the top surface and the outer peripheral surface forming a ridge line configuring a cutting edge, the cutting edge including a curved cutting corner edge portion formed at one vertex of the polygon, a first cutting edge portion contiguous to one end of the cutting corner edge portion and extending linearly, and a second cutting edge portion contiguous to the other end of the cutting corner edge portion and extending linearly, the top surface including a first rake face contiguous to the first cutting edge portion, a second rake face contiguous to the second cutting edge portion, and a third rake face contiguous to the cutting corner edge portion and also contiguous to the first and second rake faces (10, 20), the third rake face having a first region contiguous to the first rake face and a second region contiguous to the second rake face, the first rake face and the first region each having a rake angle which is a positive angle, the second rake face and the second region each having a rake angle which is a negative angle, the top surface having a third inclined surface contiguous to the first rake face, the third inclined surface being located opposite to the first cutting edge portion with the first rake face posed therebetween, and having a portion raised to have a larger distance to the seating surface as the third inclined surface is farther away from the first cutting edge portion, characterised by the cutting insert also comprising an attachment hole penetrating the cutting insert between the top surface and the seating surface, and by the first rake face having a portion that changes to have a rake angle increasing as the first rake surface approaches the third rake face. a seating surface; an outer peripheral surface contiguous to the seating surface; and a top surface contiguous to the outer peripheral surface and located opposite to the seating surface with the outer peripheral surface posed therebetween; the top surface having an external shape in a form of a polygon in a top view in which the top surface is viewed in a direction perpendicular to the seating surface and extending from the top surface toward the seating surface, the top surface and the outer peripheral surface forming a ridge line configuring a cutting edge, the cutting edge including a curved cutting corner edge portion formed at one vertex of the polygon, a first cutting edge portion contiguous to one end of the cutting corner edge portion and extending linearly, and a second cutting edge portion contiguous to the other end of the cutting corner edge portion and extending linearly, the top surface including a first rake face contiguous to the first cutting edge portion, a second rake face contiguous to the second cutting edge portion, and a third rake face contiguous to the cutting corner edge portion and also contiguous to the first and second rake faces (10, 20), the third rake face having a first region contiguous to the first rake face and a second region contiguous to the second rake face, the first rake face and the first region each having a rake angle which is a positive angle, the second rake face and the second region each having a rake angle which is a negative angle, the top surface having a third inclined surface contiguous to the first rake face, the third inclined surface being located opposite to the first cutting edge portion with the first rake face posed therebetween, and having a portion raised to have a larger distance to the seating surface as the third inclined surface is farther away from the first cutting edge portion, characterised by the cutting insert also comprising an attachment hole penetrating the cutting insert between the top surface and the seating surface, and by the first rake face having a portion that changes to have a rake angle increasing as the first rake surface approaches the third rake face.