A cutting insert based on one aspect of the present invention is provided with 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 main body (10) having a cutting edge (5) positioned at the intersection between the upper surface (2) and the side surface (4). The cutting edge (5) has an arcuate main cutting edge (51) that bows outward from the main body (10), and an arcuate auxiliary cutting edge (52) that bows outward from the main body (10) and has a smaller radius of curvature than the radius of curvature of the arcuate main cutting edge (51). A first rake part (21) sloped so as to approach the lower surface (3) in progress from the arcuate main cutting edge (51) inward to the main body (10) is provided to the upper surface (2), along the arcuate main cutting edge (51). The slope angle of the first rake part (21) decreases in progress from the portion connecting to one end part of the arcuate main cutting edge (51) toward the portion connecting to the center part of the arcuate main cutting edge (51).