PURPOSE: To stabilize tip supporting in a metal cutting throw away tool by constituting the tip as a negative rake angle type, by giving chamfer honing to a cutting edge portion so as to have specified honing width and honing angle, and by forming a projecting portion on the tip supporting surface of a seat so as to fit in the honing portion.

CONSTITUTION: Four cutting edge portions 12 are formed on an upper half surface of a tip 6 so as to extend rightwards from the corner portions at the ridges formed by an upper rake surface 8 and four clearance surfaces 10 through the chamfer honing of honing width L of 1mm or more and honing angle θof 2-15°. On the other hand, on an upper surface 28 of a seat 26, projecting portions 30 to be engaged with the rake surfaces 8 or 20 of the tip 6 are provided so as to elongate leftwards from the corner portions. In this case, an inclination angle ψ of the projecting portions 30 is determined so as to be the same as the honing angle θ of the tip 6.