A cutting insert includes a first end surface, a second end surface located opposite the first end surface and an axis extending so as to penetrate the first end surface and the second end surface. The insert includes two first cutting edges with a curve shape on a first end surface side and two second cutting edges with a curve shape on a second end surface side. Each of the first cutting edges is formed on an intersecting ridge portion between the first end surface and a corresponding side surface portion so as to curve on a plane orthogonal to the axis. Each of the second cutting edges is formed on an intersecting ridge portion between the second end surface and the corresponding side surface portion so as to curve on a plane orthogonal to the axis.