Cutting insert and cutting tool having the same

A cutting insert and a cutting tool having same. The cutting insert includes: an upper surface; a lower surface having a flat surface; a fastening hole penetrating the upper surface and the lower surface; side surfaces each connecting to the upper surface and the lower surface; and cutting edges formed by the upper surface and the side surfaces. A first cutting edge is inclined downward. A major side surface comprises a first major side surface connected to the upper surface so as to constitute the first cutting edge, and a second major side surface connected to the first major side surface and the lower surface. A minor side surface comprises a first minor side surface connected to the upper surface so as to constitute a second cutting edge, and a third minor side surface connected to the upper surface and the lower surface.