To provide a method for producing the subject compound on an industrial scale, which does not produce large quantities of metal oxides handled as an industrial waste and enables by-product sulfur dioxide to be utilized in the production process.

This compound is obtained by diazotizing sulfanilamide hydrochloride with sodium nitrite followed by reduction with an aqueous solution of sodium bisulfite and sodium sulfite and then hydrolyzing the reaction product with hydrochloric acid.