A method for producing an isocyanate, from using an organic primary amine, urea and an aromatic hydroxy compound as raw materials, comprising: a carbamation step of generating an N-substituted carbamate from the organic primary amine, the urea and the aromatic hydroxy compound according to a carbamation reaction, and then recovering a first gaseous phase component containing the urea and/or a compound having a carbonyl group derived from the urea, the aromatic hydroxy compound, and ammonia; a condensation step of condensing the first gaseous phase component with a condenser; an isocyanate production step of producing an isocyanate by subjecting the N-substituted carbamate to pyrolysis; an ammonia absorption step of allowing a second gaseous phase component containing ammonia recovered as a gaseous phase component from the condenser as a main component, to be absorbed by absorption water, and generating gas-absorbed water; and an ammonia stripping step of heating the gas-absorbed water to separate the ammonia from the gas-absorbed water; wherein ammonia obtained in the ammonia stripping step is further burned to recover heat, and the thus recovered heat is used as a heat source in the carbamation step and/or the isocyanate production step, wherein the second gaseous phase component contains urea and/or isocyanic acid, and an aromatic hydroxy compound, and the gas-absorbed water contains ammonia, urea and/or isocyanic acid, and an aromatic hydroxy compound, wherein a liquid phase component obtained after the separation of the ammonia in the ammonia stripping step contains an aromatic hydroxy compound and a water phase, and the aromatic hydroxy compound is separated from the water phase according to phase separation, wherein the method further comprises an aromatic hydroxy compound separation step of separating an aromatic hydroxy compound and a water phase, both contained in a liquid phase component obtained after the separation of the ammonia in the ammonia stripping step, and a liquid phase blow-down step of substituting a portion of an aqueous solution obtained in the aromatic hydroxy compound separation step with water. a carbamation step of generating an N-substituted carbamate from the organic primary amine, the urea and the aromatic hydroxy compound according to a carbamation reaction, and then recovering a first gaseous phase component containing the urea and/or a compound having a carbonyl group derived from the urea, the aromatic hydroxy compound, and ammonia; a condensation step of condensing the first gaseous phase component with a condenser; an isocyanate production step of producing an isocyanate by subjecting the N-substituted carbamate to pyrolysis; an ammonia absorption step of allowing a second gaseous phase component containing ammonia recovered as a gaseous phase component from the condenser as a main component, to be absorbed by absorption water, and generating gas-absorbed water; and an ammonia stripping step of heating the gas-absorbed water to separate the ammonia from the gas-absorbed water; wherein ammonia obtained in the ammonia stripping step is further burned to recover heat, and the thus recovered heat is used as a heat source in the carbamation step and/or the isocyanate production step, wherein the second gaseous phase component contains urea and/or isocyanic acid, and an aromatic hydroxy compound, and the gas-absorbed water contains ammonia, urea and/or isocyanic acid, and an aromatic hydroxy compound, wherein a liquid phase component obtained after the separation of the ammonia in the ammonia stripping step contains an aromatic hydroxy compound and a water phase, and the aromatic hydroxy compound is separated from the water phase according to phase separation, wherein the method further comprises an aromatic hydroxy compound separation step of separating an aromatic hydroxy compound and a water phase, both contained in a liquid phase component obtained after the separation of the ammonia in the ammonia stripping step, and a liquid phase blow-down step of substituting a portion of an aqueous solution obtained in the aromatic hydroxy compound separation step with water.