PURPOSE: To increase durability and lengthen life at a low cost by mixing partially cutting edges having edges made of high abrasion proof sintered diamond in plural cutting edges of a conventional rotary carbide cutter and designing a shape of the edges.

CONSTITUTION: Among cutting edges 1W10, the cutting edges 3, 6 and 9 are diamond cutting edges and the remaining cutting edges 1, 2, 4, 5... are made of either carbide or high speed steel. Thus one cutting edge made of highly abrasion proof diamond is provided to every two cutting edges made of high speed steel. Then, in applying a sintered diamond to the cutter edge, not only a change of material from a conventional carbide cutter edge to the sintered diamond one but also the change of the tool shape is carried out. Namely, as for radial rake angles θ1 and θ2 of each cutting edge, θ1 is zero or plus value in the cutting edges 1, 2, 4, 5... and θ2 is zero or minus value in the cutting edges 3, 6.... With this the durability is increased and life is lengthened at a low cost.