PURPOSE: To enable the production at a high-temperature under a high pressure such as those of hot isostatic pressing without using a capsule therein, simplification of a process and formation of a near net shape by coating grains such as diamond to be a core with a substance capable of forming a peripheral structure and further the peripheries of the grains with a binding phase in a method for producing a sintered compact comprising an ultrahigh-pressure phase such as the diamond and/or cubic BN.

CONSTITUTION: This sintered compact of an ultrahigh-pressure phase having a three-phase structure comprises the three-phase structure of a core part, a peripheral structure and a binding phase. The core part comprises the ultrahigh- pressure phase such as diamond and/or cubic BN and the peripheral structure comprises one or more of carbides, nitrides, oxides, borides of group IVa, Va and VIa elements of the periodic table and Al and compounds thereof. The binding phase comprises one or more of carbides, nitrides, oxides, borides of group IIA, IVa, Va and VIa elements of the periodic table, Sr, Ba and Al and compounds thereof or Fe family metals.