A cutting insert may have an upper surface, lower surface, side surface, and a polygonal plate shaped to form a cutting edge at a ridgeline where the upper surface and the side surface intersect. The upper surface has a major part having a flat upper end surface, a first protrusion protruding from the major part toward a corner part of the upper surface, a second protrusion protruding from the first protrusion toward the corner part, and a pair of projections located between the second protrusion and the cutting edge. A height of an upper end of the first protrusion from the lower surface is lower than a height of the upper end surface of the major part and is higher than a height of the cutting edge. A height of an upper end of the second protrusion from the lower surface is equal to the height of the cutting edge.