An object of the present invention is to provide a process that enables isocyanate to be produced stably over a long period of time and at high yield without encountering problems of the prior art during production of isocyanate without using phosgene. The present invention discloses a process for producing an isocyanate by subjecting a carbamic acid ester to a thermal decomposition reaction, including the steps of: recovering a low boiling point component in a form of a gaseous phase component from a thermal decomposition reaction vessel in which the thermal decomposition reaction is carried out; recovering a liquid phase component containing a carbamic acid ester from a bottom of the thermal decomposition reaction vessel; and supplying all or a portion of the liquid phase component to an upper portion of the thermal decomposition reaction vessel.