A cutting insert (10, 100), comprising: two opposed end surfaces (20a, 20b) including a first end surface and a second end surface, the first end surface comprising a first surface, a back side of the first surface being a second surface, the second surface being 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 the first end surface and the peripheral side surface, wherein: the plurality of cutting edge portions is arranged so as to have a rotational symmetry about a first axis which passes through the two end surfaces; and an intermediate plane, which is perpendicular to the first axis and passes through the peripheral side surface, is defined; characterized in that: each cutting edge portion includes: a corner edge formed at a corner of the first end surface; a major cutting edge extending from one end of the corner edge, and extending so that a distance between the major cutting edge and the intermediate plane becomes longer than a distance between the first surface and the intermediate plane; and a minor cutting edge extending from the other end of the corner edge, and extending so that a distance between the minor cutting edge and the intermediate plane becomes shorter than a distance between the first surface and the intermediate plane. two opposed end surfaces (20a, 20b) including a first end surface and a second end surface, the first end surface comprising a first surface, a back side of the first surface being a second surface, the second surface being 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 the first end surface and the peripheral side surface, wherein: the plurality of cutting edge portions is arranged so as to have a rotational symmetry about a first axis which passes through the two end surfaces; and an intermediate plane, which is perpendicular to the first axis and passes through the peripheral side surface, is defined; the plurality of cutting edge portions is arranged so as to have a rotational symmetry about a first axis which passes through the two end surfaces; and an intermediate plane, which is perpendicular to the first axis and passes through the peripheral side surface, is defined; each cutting edge portion includes: a corner edge formed at a corner of the first end surface; a major cutting edge extending from one end of the corner edge, and extending so that a distance between the major cutting edge and the intermediate plane becomes longer than a distance between the first surface and the intermediate plane; and a minor cutting edge extending from the other end of the corner edge, and extending so that a distance between the minor cutting edge and the intermediate plane becomes shorter than a distance between the first surface and the intermediate plane. a corner edge formed at a corner of the first end surface; a major cutting edge extending from one end of the corner edge, and extending so that a distance between the major cutting edge and the intermediate plane becomes longer than a distance between the first surface and the intermediate plane; and a minor cutting edge extending from the other end of the corner edge, and extending so that a distance between the minor cutting edge and the intermediate plane becomes shorter than a distance between the first surface and the intermediate plane.