PURPOSE: To produce an isocyanate compound economically and efficiently without using poisonous phosgene by using a formamide compound or an amine compound as main raw materials.

CONSTITUTION: A formamide compound is reacted with dimethyl carbonate in the presence of an alkali catalyst or methyl formate is reacted with an amine compound and dimethyl carbonate. A prepared urethane compound is thermally decomposed in an inert solvent having a higher boiling point than a formed isocyanate compound under 1-150mmHg reduced pressure at 150-350°C without using a catalyst and mixed vapor of formed methanol and a corresponding isocyanate compound is partially condensed.