A milling insert includes a polygonal tubular insert body which has: rake faces on one polygonal surface thereof, flanks composed of circumferential surfaces adjacent to the polygonal surface, and cutting edges defining a ridge line where the rake faces and flanks intersect each other as cutting edges. The rake faces have serrations where mount portions and valley portions are arrayed alternately to intersect the cutting edges. The ridge line has a waveform shape when the flanks are viewed from above. Bottom portions and top portions of the waveform are formed into concave circular arc portions and convex circular arc portions, respectively, and are alternately repeated. Both of the concave and convex circular arc portions are a ¼ circular arc or more to a ⅓ circular arc or less. Each of the concave circular arc portions is unevenly located between the convex circular arc portions adjacent thereto.