To provide a cutting insert with excellent wear resistance and chipping resistance, a tool unit, a cutting insert manufacturing method, and a ceramic manufacturing method.

The cutting insert 1 is e.g. a chip of SNGN120412 according to JIS or the like, and formed of an alumina sintered body mainly consisting of alumina and containing 0.02-2.0 mol.% group 3A metal oxide (for example, Yb2O3). The cutting insert 1 can be used with both faces 3 and 5 as main surface sides (both faces in the vertical direction in the figure) as rake faces, respectively, and the fracture toughness value of the faces 3 and 5 on both rake face sides is at least two times the fracture toughness value at a core portion (for example, at 100μm from the face 3).