A cutting insert comprising a cutting edge formed by an intersection ridge between a rake face and a side face, the cutting edge including a major cutting edge, a flat cutting edge, and a chamfer edge disposed between the major cutting edge and the flat cutting edge, wherein in a direct view of a side face near the flat cutting edge, a ratio of installation area length L2 of the chamfer edge to installation area length L3 of the major cutting edge is L2:L3=2:8 to 5:5, and inclination angle θ1 of the chamfer edge with respect to the flat cutting edge and inclination angle θ2 of the major cutting edge with respect to the flat cutting edge are set to have a relationship of θ1