Cutting insert and cutting method

A cutting insert, wherein:

• a cutting edge part having a quadrangular shaped cutting face, which is provided with a pair of side cutting edges extending in a longitudinal direction of an insert body, and a front cutting edge between ends of the side cutting edges that extends in a direction that intersects the longitudinal direction, is formed at an end of the insert body having a bar-shape;
• and
• viewed from a direction facing the cutting face perpendicularly to the longitudinal direction, at least one of a pair of corner edges where the side cutting edge and the front cutting edge intersect is formed in a convex shape such that it has a point of inflection at which, after a tangent line that makes contact with the corner edge rotates in a direction extending in the longitudinal direction along the corner edge from the front cutting edge, its direction of rotation changes, and it joins the side cutting edge, characterized in that
• the corner edge comprises, in order, from the front cutting edge towards the side cutting edges at each of the corners:
• a convex-curved line edge with a convex arc shape of approximately one fourth of a circle that merges smoothly with the front cutting edge;
• a wiper edge that merges with the convex-curved line edge and extends in a straight line in the longitudinal direction;
• and
• a straight line edge that is angled such that it is indented toward the inside of the cutting face in the widthwise direction of the insert main body as it approaches the side cutting edge,
• wherein the incline angle α of the straight line edge with respect to the axis of the insert body is in a range of 30° to 90°.