PURPOSE: To impart such various characteristics as strength, toughness, workabilty, hardness and wear resistance required by a cutting tool to a sintered compact by using carbide or nitride of a transition metal, an iron family metal and amorphous diamond powder in a certain ratio as the constituents of the sintered compact.

CONSTITUTION: The compsn. of this sintered compact consists of, by volume, 20-85% carbide, nitride or boride of a group IVa, Va or VIa transition metal of the Periodic Table or mixture or solid soln. of such compds., 2-30% iron family metal and 10-50% polycrystalline diamond of 1-40μm grain size, and carbon has been deposited in the iron family metal or on the surface of the metal. This sintered compact is produced by sintering a starting material mixture at 950-1,150°C under 1-30kbar pressure optionally after reduction treatment in a reducing atmosphere at 500-900°C.