An insert, comprising: an upper surface comprising a corner part; a lower surface; a side surface located between the upper surface and the lower surface; and a cutting edge located at least at a part of a region in which the upper surface and the side surface intersect each other, and comprising: a first cutting edge located at the corner part; a second cutting edge adjacent to the first cutting edge; a third cutting edge adjacent to the second cutting edge; and a fourth cutting edge adjacent to the third cutting edge, wherein each of the third cutting edge and the fourth cutting edge has a concave curvilinear shape extending downward in a side view, and a radius of curvature of the fourth cutting edge is smaller than a radius of curvature of the third cutting edge, wherein the upper surface further comprises an inclined surface being inclined downward as going farther from the cutting edge, wherein the inclined surface comprises: a first inclined surface located along the first cutting edge; a second inclined surface located along the second cutting edge; a third inclined surface located along the third cutting edge; and a fourth inclined surface located along the fourth cutting edge, characterised in that an inclination angle of each of the third inclined surface and the fourth inclined surface is larger than an inclination angle of the second inclined surface. an upper surface comprising a corner part; a lower surface; a side surface located between the upper surface and the lower surface; and a cutting edge located at least at a part of a region in which the upper surface and the side surface intersect each other, and comprising: a first cutting edge located at the corner part; a second cutting edge adjacent to the first cutting edge; a third cutting edge adjacent to the second cutting edge; and a fourth cutting edge adjacent to the third cutting edge, wherein each of the third cutting edge and the fourth cutting edge has a concave curvilinear shape extending downward in a side view, and a radius of curvature of the fourth cutting edge is smaller than a radius of curvature of the third cutting edge, a first cutting edge located at the corner part; a second cutting edge adjacent to the first cutting edge; a third cutting edge adjacent to the second cutting edge; and a fourth cutting edge adjacent to the third cutting edge, wherein each of the third cutting edge and the fourth cutting edge has a concave curvilinear shape extending downward in a side view, and a radius of curvature of the fourth cutting edge is smaller than a radius of curvature of the third cutting edge, wherein the upper surface further comprises an inclined surface being inclined downward as going farther from the cutting edge, wherein the inclined surface comprises: a first inclined surface located along the first cutting edge; a second inclined surface located along the second cutting edge; a third inclined surface located along the third cutting edge; and a fourth inclined surface located along the fourth cutting edge, characterised in that an inclination angle of each of the third inclined surface and the fourth inclined surface is larger than an inclination angle of the second inclined surface. a first inclined surface located along the first cutting edge; a second inclined surface located along the second cutting edge; a third inclined surface located along the third cutting edge; and a fourth inclined surface located along the fourth cutting edge, characterised in that an inclination angle of each of the third inclined surface and the fourth inclined surface is larger than an inclination angle of the second inclined surface.