The present invention relates to a cutting insert. The cutting insert, according to one embodiment of the present invention, comprises: a top surface; a bottom surface; side surfaces which connect the top surface and the bottom surface to each other; a hole which penetrates the top surface and the bottom surface; and cutting edges which are defined by the top surface and the side surfaces, wherein a main cutting edge side surface among the side surfaces is provided with a first relief surface, a transition surface extending from the first relief surface, and a second relief surface extending from the transition surface, the first relief surface is formed such that the relief angle or the relief surface width varies along the cutting edge, and the transition surface is provided with a plurality of ridges in order to reinforce the rigidity of the cutting edge.

A cutting insert has an upper surface, a lower surface and a lateral surface. The upper surface has a first upper side, and a second upper side. The lower surface has a first lower side and a second lower side. The lateral surface has a first lateral surface, a second lateral surface, and a third lateral surface. The first lateral surface has a first concave part having a first constraining surface having a flat shape. The second lateral surface has a second concave part having a second constraining surface having a flat shape. The third lateral surface has a convex part. The first concave part and the second concave part are separated from each other by the convex part.