The first cutting insert is attached to a first pocket. The second cutting insert is attached to a second pocket. The third cutting insert is attached to a third pocket. The first pocket has a first seat surface, a second seat surface, a third seat surface, and a first swarf discharging groove. The second pocket has a fourth seat surface, a fifth seat surface, a sixth seat surface, and a second swarf discharging groove. The third pocket has a seventh seat surface, an eighth seat surface, a ninth seat surface, and a third swarf discharging groove. In a cross section perpendicular to an axis, an angle formed between a straight line along the sixth seat surface and a tangent of the second swarf discharging groove at a boundary between the outer circumferential surface and the second swarf discharging groove is more than 90°.