A throw-away insert includes: an upper surface; a bottom surface; two side surfaces formed with upper side surfaces and lower side surfaces; two end surfaces; four nose sections formed at the corners of the upper surface; a main cutting section formed from a ridge line positioned at the intersection between the upper side surface and the upper surface; a secondary cutting section formed from a linear ridge line positioned at the intersection between the end surface and the upper surface; and an axial support surface formed from a section of the end surface. The upper side surface is projected outward more than the lower side surface.