The present invention addresses the problem of providing, in order to reduce burrs on the corners of machined surfaces in face milling, a cutting insert with which burrs are not easily generated. A cutting insert for milling comprising a cutting edge (5) formed from the intersection ridges of the upper and lower surfaces (2, 4) with the side surface (3), said cutting edge comprising a flat cutting edge (5b). The cutting edge (5) is configured from a main cutting edge (5a) formed between adjacent corners, a flat cutting edge (5b) formed on the corner, and a minor cutting edge (5c) formed between the main cutting edge and the flat cutting edge. The surface roughness of the side surface (3a) that is continuous with the main cutting edge (5a) is made to be rougher than the surface roughness of the side surface (3c) that is continuous with the minor cutting edge (5c).