A cutting insert for cutting off or grooving, comprising: a leading cutting edge having a rake angle (θ) in the range of 20° to 35° in a central region in a width direction; and a rake face having a breaker groove formed in the central region in the width direction and land portions formed in both end regions in the width direction, wherein the land portions have a rake angle smaller than the rake angle in the central region in the width direction, and wherein the breaker groove includes opposing side faces separated from each other by a distance that decreases with increasing distance from the leading cutting edge and four shoulder portions (10b, 10c) of the same height that are formed on the opposing side faces at positions above the land portions, two of the shoulder portions being closer to the leading cutting edge and to outer sides in the width direction than the other two shoulder portions are, wherein inclined faces being curved upward toward a top face are connected to back portions of the land portions, wherein the opposing side faces are extended upward from the bottom of the breaker groove, wherein inclined faces are extended upward from a bottom of the breaker groove at relief portions, and groove side surfaces are formed in a region where the width of the breaker groove is reduced, and intersect the inclined faces that extend upward from the bottom of the breaker groove at the relief portions, wherein two of the shoulder portions that are closer to the leading cutting edge are formed at the positions where the inclined faces, the top face, and the opposing side faces intersect, characterized in that the remaining two of the shoulder portions are formed at the positions where the inclined faces that extend upward from the bottom of the breaker groove at the relief portions, the groove side surfaces, and the top face intersect. a leading cutting edge having a rake angle (θ) in the range of 20° to 35° in a central region in a width direction; and a rake face having a breaker groove formed in the central region in the width direction and land portions formed in both end regions in the width direction, wherein the land portions have a rake angle smaller than the rake angle in the central region in the width direction, and wherein the breaker groove includes opposing side faces separated from each other by a distance that decreases with increasing distance from the leading cutting edge and four shoulder portions (10b, 10c) of the same height that are formed on the opposing side faces at positions above the land portions, two of the shoulder portions being closer to the leading cutting edge and to outer sides in the width direction than the other two shoulder portions are, wherein inclined faces being curved upward toward a top face are connected to back portions of the land portions, wherein the opposing side faces are extended upward from the bottom of the breaker groove, wherein inclined faces are extended upward from a bottom of the breaker groove at relief portions, and groove side surfaces are formed in a region where the width of the breaker groove is reduced, and intersect the inclined faces that extend upward from the bottom of the breaker groove at the relief portions, wherein two of the shoulder portions that are closer to the leading cutting edge are formed at the positions where the inclined faces, the top face, and the opposing side faces intersect, characterized in that the remaining two of the shoulder portions are formed at the positions where the inclined faces that extend upward from the bottom of the breaker groove at the relief portions, the groove side surfaces, and the top face intersect.