A method for producing methionine comprising a hydantoin step of reacting 3-methylmercaptopropionaldehyde and hydrocyanic acid, or a compound obtained by reacting 3-methylmercaptopropionaldehyde and hydrocyanic acid, with carbon dioxide and ammonia to obtain a liquid containing 5-(2-methylmercaptoethyl)hydantoin, a hydrolysis step of hydrolyzing the 5-(2-methylmercaptoethyl)hydantoin, a crystallization step of introducing carbon dioxide into a liquid containing a methionine salt obtained in the hydrolysis step to precipitate methionine, and a separation step of separating a methionine slurry obtained in the crystallization step into solid and liquid, the method comprising: a removal step of blowing an inert gas into the liquid containing the 5-(2-methylmercaptoethyl)hydantoin and thereby diffusing ammonia remaining in the liquid to obtain an emission gas containing the ammonia; and a recovery step of bringing the emission gas into contact with a washing liquid to recover ammonia contained in the emission gas, wherein the recovery step comprises at least one step selected from the group consisting of a first step in which ammonium carbonate water is used as the washing liquid to dissolve ammonia contained in the emission gas into the ammonium carbonate water, and a second step in which water is circulated and used as the washing liquid to dissolve ammonia contained in the emission gas into the water. a hydantoin step of reacting 3-methylmercaptopropionaldehyde and hydrocyanic acid, or a compound obtained by reacting 3-methylmercaptopropionaldehyde and hydrocyanic acid, with carbon dioxide and ammonia to obtain a liquid containing 5-(2-methylmercaptoethyl)hydantoin, a hydrolysis step of hydrolyzing the 5-(2-methylmercaptoethyl)hydantoin, a crystallization step of introducing carbon dioxide into a liquid containing a methionine salt obtained in the hydrolysis step to precipitate methionine, and a separation step of separating a methionine slurry obtained in the crystallization step into solid and liquid, the method comprising: a removal step of blowing an inert gas into the liquid containing the 5-(2-methylmercaptoethyl)hydantoin and thereby diffusing ammonia remaining in the liquid to obtain an emission gas containing the ammonia; and a recovery step of bringing the emission gas into contact with a washing liquid to recover ammonia contained in the emission gas, wherein the recovery step comprises at least one step selected from the group consisting of a first step in which ammonium carbonate water is used as the washing liquid to dissolve ammonia contained in the emission gas into the ammonium carbonate water, and a second step in which water is circulated and used as the washing liquid to dissolve ammonia contained in the emission gas into the water. a removal step of blowing an inert gas into the liquid containing the 5-(2-methylmercaptoethyl)hydantoin and thereby diffusing ammonia remaining in the liquid to obtain an emission gas containing the ammonia; and a recovery step of bringing the emission gas into contact with a washing liquid to recover ammonia contained in the emission gas, wherein the recovery step comprises at least one step selected from the group consisting of a first step in which ammonium carbonate water is used as the washing liquid to dissolve ammonia contained in the emission gas into the ammonium carbonate water, and a second step in which water is circulated and used as the washing liquid to dissolve ammonia contained in the emission gas into the water.