A main raw material powder comprising cobalt oxide powder, chromium oxide powder and carbon powder is added with at least one metal oxide powder selected from the group consisting of manganese oxide powder, vanadium oxide powder, titanium oxide powder, tantalum oxide powder, niobium oxide powder, boron oxide powder, hafnium oxide powder, tungsten oxide powder, molybdenum oxide powder, iron oxide powder, nickel oxide powder and copper oxide powder; these powders are then mixed and pulverized to prepare a mixed powder; said mixed powder is then reduced by heating under vacuum or in a reducing atmosphere to obtain a reduced sponge-like mass; said sponge-like mass is finely pulverized, thereby manufacturing a cobalt-base reduced powder.A cobalt-base sintered alloy, produced by using said cobalt-base reduced powder thus manufactured as the material powder, has a relatively wide range of diffusion sintering temperatures applicable at the time of sintering thereof and has furthermore a high sintered density.