PURPOSE: To sufficiently develop drilling capacity of a diamond bit by forming an abrasion-resistant reinforcing zone to the inner and outer diameter part of the leading end of the diamond bit.

CONSTITUTION: A size is preliminarily thinly applied to the part to be reinforced inside the recessed part of a carbon mold 6 forming the reinforcing zone 20 of an inner and outer diameter part before the recessed part is packed with a filling powder 13. Next, in order to form the reinforcing zone 20, for example, the recessed part is packed with a mixed powder, that is, a hardening powder consisting of a relatively coarse hard alloy powder with a particle size of 40-80 mesh and usual size diamond with a particle size of 30-60 mesh and, subsequently, the carbon mold 6 is turned over and the excessive hardening powder is discharged excepting the hardening powder bonded to the size. Next, the recessed part is packed with a usual internal filler 13, for example, composed of WC with a particle size of 1-10μm, 2-10% of Ni with a particle size of 1-20μm and diamond with a particle size of 30-60 mesh and, thereafter, a binder alloy 18 consisting of 20-90% of Cu, 15-40% of Ni and 5-40% of Mn is placed on an upper carbon mold to perform sintering in an inert atmosphere furnace under heating.