PURPOSE: To increase power, securely holding a diamond grain, and eliminate looseness or destone even for diamond of small grain, by performing soft nitriding treatment to a binding agent consisting of iron, steel or metal containing iron.

CONSTITUTION: The method of normal electrolytic plating or sintering is applied as the method of fixing a diamond particle 1, to increase binding power of a binding agent 2 consisting of iron, steel or metal containing iron obtained from said method, soft nitriding treatment is applied. The method of soft nitriding treatment is performed in such a manner that nitrogen and carbon are diffused and infiltrated to iron or steel and hardened by heating to temperatue about 570°C in cemented nitride gas mainly composed of NH3 and CO.