A cutting edge is formed at a ridge between an upper surface and a side surface. In the side surface, a plurality of grooves are formed so as to extend from the side surface to the upper surface to divide the cutting edge, and the clearance angles within these grooves are formed so as to increase from one end of the cutting edge toward the other end of the cutting edge. This achieves a cutting insert having small cutting force and excellent cutting performance. Among the plurality of grooves, the groove nearest to the one end of the cutting edge has preferably a width increasing from the upper surface of the cutting insert toward the lower surface.