Cutting insert for drill, drill, and method of cutting using the same

A cutting insert for a drill, comprising:

• an upper face comprising a first corner portion, and a first side and a second side respectively disposed on both sides of the first corner portion;
• a bottom face corresponding to the upper face;
• a side face located between the upper face and the bottom face;
• a first cutting edge formed along the first side;
• and
• a second cutting edge formed along the second side, wherein
• the side face comprises a first region which is connected to the first cutting edge, a second region which is connected to the second cutting edge, and a third region corresponding to the first corner portion,
• the third region comprises an upper region which is adjacent to the first corner portion and is disposed toward the upper face, and a lower region located below the upper region and connected to the upper region, and
• an inclination angle θ3 of the lower region to the bottom face is larger than each of an inclination angle θ1 of the first region to the bottom face and an inclination angle θ2 of the second region to the bottom face,
• the inclination angle θ2 is larger than the inclination angle θ1,
• an inclination angle θ4 of the upper region to the bottom face increases as it goes from the first region to the second region, and
• the inclination angle θ3 is constant in a direction along the first corner portion.