CUTTING INSERT

Provided is a cutting insert, which has excellent chip discharge performance even when formed with multiple corners superior in economic efficiency. A first ridgeline (R1) at which an upper surface (5) and a circumferential side surface (7) intersect each other includes a plurality of corners (A, B, C, D, E, F, G, H) disposed at equal intervals and a plurality of main cutting edges (50) disposed one by one between the corners adjacent to each other. A distance between the corners adjacent to each other is equal to or less than 60% of the diameter of a circle inscribed within the ridgeline. The main cutting edges includes a first cutting edge (51) that is linearly formed and a second cutting edge (52) that is linearly formed. The length (L2) of the second cutting edge is equal to or less than half the length (L1) of the first cutting edge and is positioned closer to a center side of the cutting insert than an extension line of the first cutting edge is. The circumferential side surface includes a first side surface (71) facing the first cutting edge and a second side surface (72) facing the second cutting edge. A clearance angle (α) of the first side surface is smaller than that (β) of the second side surface.