PURPOSE: To obtain the title compound by reacting an isophoronediamine with phosgene, distilling a reaction mixture and heat-treating to reduce the amount of hydrolyzable chlorine and acidity of the mixture.

CONSTITUTION: Isophoronediamine and/or its hydrochloride is reacted with phosgene in an inert solvent (e.g. decalin) at 50-170°C for 1-20 hours. Then the reaction mixture is degassed by introducing an inert gas (e.g. N2gas) and further distilled to distill away the inner solvent. Successively, the resulting substance is heat-treated at 160-270°C for 0.1-5 hours to give the objective high-purity substance. When the objective substance is used as a polyurethane raw material, reaction rate in polymerization and function of formed polyurethane are stabilized and maintained at high level.