A throw-away insert includes: an upper and bottom surface; two side surfaces; two end surfaces; a main cutting section formed from a ridge line positioned at the intersection between the side surfaces and the upper surface; a secondary cutting section formed from a ridge line positioned at the intersection between the end surfaces and the upper surface; an axial support surface supported by an insert pocket of a cutter body; and noses formed at the corners of the upper surface. The corner angles of the noses when seen from above are essentially right angles. The axial support surface is formed as a section of the end surface. The secondary cutting section is parallel to the ridge line at the upper end of the axial support surface and the bottom surface. The upper end of the axial support surface is positioned so that it is projected more in the direction of the longitudinal axis of the main cutting section than the ridge line of the upper end.