To produce the subject hydrochloride in a high yield while facilitating the control of reactional temperature and excellent in operations by adding a nitrile compound to an alcohol solution containing hydrogen chloride dissolved therein.

(C) A nitrile compound (e.g. acetonitrile) is added to (B) an alcohol solution (e.g. methanol) containing (A) hydrogen chloride (e.g. hydrogen chloride gas) dissolved therein. Furthermore, the internal temperature of the solution of the component B containing the component A dissolved therein is preferably within the range of -10 to +20°C and the component A is used in an amount of preferably 0.8-3.0 mol based on 1 mol of the component C. The component B is used in an amount of preferably 1.0-3.0 mol based on 1 mol of the component C. For example, the component C sufficiently dehydrated with a dehydrating agent such as phosphorus pentoxide is preferably added and the internal temperature is preferably kept at a temp. of 0-20°C to age the reactional mixture for about 1-20 h under stirring.