PURPOSE: To provide a polygonal indexable cutting insert having a positive rake.

CONSTITUTION: An insert 10 comprises an upper surface 12; a bottom surface 14; a side wall 16 stretching between the upper surface and the bottom surface substantially with no break. Each side flank crosses a bottom in the position of an edge part 24 and crosses the upper surface in the position of an edge part 26 and the side flank crosses a bottom edge at an obtuse angle and crosses an upper edge at a slight acute angle. A cross part between the side flank and the upper surface forms a cutting edge 28. A plurality of preferably sine- curve-form serrations are formed at each cutting edge of the insert at equal intervals. The center line of the sine curve is separated away from each other.