A cutting insert has an upper surface, a lower surface, a side surface connected to each of the upper surface and the lower surface, and a cutting edge having sequentially a corner cutting edge, a first straight cutting edge, a second straight cutting edge, and a third straight cutting edge, which are located along an intersection of the upper surface and the side surface and intersect one another at an obtuse angle. The upper surface has a first inclined surface extending along the first straight cutting edge, a second inclined surface extending along the second straight cutting edge, and a third inclined surface extending along the third straight cutting edge. An inclination angle of the second inclined surface with respect to the lower surface is larger than an inclination angle of each of the first inclined surface and the third inclined surface with respect to the lower surface.