This cutting insert has a rake surface, a relief surface, and a seat surface. A cutting edge includes a nose section, a first cutting edge section, and a second cutting edge section. The rake surfaceis provided with a first protrusion, a second protrusion, a third protrusion, and a fourth protrusion. If the boundary between a first sloped section and a first breaker section, the boundary betweena first stepped surface and a second breaker section, the boundary between a second sloped section and a third breaker section, and the boundary between a second stepped surface and a fourth breaker section are respectively defined as a first position, a second position, a third position, and a fourth position, then, in the direction perpendicular to the seat surface, the second position is higherthan the first position, and the fourth position is higher than the third position, and in the direction parallel to the seat surface, the distance between the first position and the third position is greater than the distance between the second position and the fourth position.