To provide a cutting insert reduced in dimensional error in a machining surface and superior in machining accuracy in three dimensional machining, in particular.

The cutting insert 1 includes an upper surface 2, a lower surface 3, a side surface 4 connected to the upper surface 2 and the lower surface 3, and a cutting blade 5 positioned at a crossing part of the upper surface 2 and the side surface 4. The cutting blade 5 has a plurality of first circular arc-shaped cutting blades 51 projected at an outer side of a body, and a plurality of second circular arc-shaped cutting blades 52 having smaller curvature radii than those of the first circular arc-shaped cutting blades 51. The plurality of first circular arc-shaped cutting blades 51 and the plurality of second circular arc-shaped cutting blades 52 are disposed alternately. The first circular arc-shaped cutting blades 51 are curved to a side away from the lower surface 3 in a side view. Compared with circular arc-shaped cutting blades having one curvature radius, the curvature radii of the first circular arc-shaped cutting blades 51 can be set larger, and a machining surface higher in working accuracy can be obtained than the case that the cutting blades are advanced in multiple directions.