A cutting insert includes two end surfaces each having a main surface usable as an attachment surface to a tool body, a peripheral side surface extending between the two end surfaces and a plurality of cutting edge portions each formed at an intersection between each end surface and the peripheral side surface. Each cutting edge portion includes a corner edge formed at a corner of a related end surface, a major cutting edge extending from one end of the corner edge and extending so as to depart from an intermediate plane defined to be perpendicular to the first axis and to include the second axis, and a minor cutting edge extending from the other end of the corner edge and extending in a direction to approach the intermediate plane.