A cutting insert includes an upper surface, a lower surface, a side surface, a cutting edge, and a groove portion. The cutting edge includes a main cutting edge, an auxiliary cutting edge arranged so as to make an obtuse angle to the main cutting edge in the upper surface view, and a corner cutting edge positioned between the main cutting edge and the auxiliary cutting edge and is located in at least a part of an intersection portion between the upper surface and the side surface. The groove portion is located on the side surface so as to reach the upper surface. In this cutting insert, a side wall surface of the groove portion positioned on the side near the corner cutting edge is substantially parallel to the auxiliary cutting edge or comes close to the auxiliary cutting edge toward inside of the groove portion in the upper surface view.