To provide a method for producing an organic isocyanate with a high yield, without using phosgene.

There is provided a production method for an organic isocyanate, comprising a step of reacting a quaternary ammonium cyanate with an alcohol, in an aprotic organic solvent in the presence of phosphonium betaine obtained by reacting 2,3-dichloro-5,6-dicyano-p-benzoquinone with a phosphine compound. As the phosphine compound, in which all hydrogen atoms of phosphorus hydride are substituted with 1-10C alkyl, 6-10C aryl and/or 7-10C aralkyl, is preferable, and as the quaternary ammonium cyanate, in which quaternary nitrogen atom is bonded only with 1-15C alkyl, is preferable.