PURPOSE: To enable diamond particles to be applicable to all uses such as adjusting characteristics such as strength, etc., drill bits, dressers, etc., by coating granules containing diamond particles and its sintering auxiliary.

CONSTITUTION: This production method of sintered diamond particles is to knead and granulate a mixture of powdery diamond in any state of fine powder, crude powder or mixture powder with a sintering auxiliary for cutting tools or converting graphite to diamond by a method such as a spray drying, a wet compressive extruding granulation, etc., by adding a solvent, supply a slurry in which powdery inactive materials such as a metal oxide or a nitride which does not react with the granules 1 are suspended or a solution in which the inactive materials are dissolved in a liquid and obtain coated particles 3 or a compacted body 4 prepared by compress molding through a cold isotropic compression. One or more of the coated particles 3 or compacted body 4 are kept in a thermodynamically stable region and the sintered diamond particles can be obtained by baking at about 1450°C for about 15min. using a monoaxial type super high pressure device.