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 . <EOS>