A cutting insert including a surface involved in cutting, for which a cutting tool material of a hard sintered body is used. A radius of a nose R portion is 0.4 mm or greater and 2.4 mm or less, an apex angle α of the nose R portion is 50° or greater and 95° or less, a rake angle β at a position of a bisecting plane of the apex angle of the nose R portion is 1° or greater and 10° or less, a chamfer provided in a cutting edge portion is a negative land with unequal width, and at least on one side of the negative land with respect to a boundary which is an apex of a nose R portion cutting edge, a width of the negative land gradually decreases from the apex of the nose R portion cutting edge to a position at which the nose R portion cutting edge is connected to a linear cutting edge. Let W1 be the width of the negative land at the apex of the nose R portion cutting edge, and W2 be the width of the negative land at both ends of the nose R portion cutting edge, then the W1 is 0.04 mm or greater and 0.2 mm or less, and a ratio of the W1 1 to the W2 is 1.5 or greater.