To obtain a primary amine, without forming any waste salt impossible to reuse and wastewater difficult to biodegrade by reacting a precursor compound for carbenium ion with a nitrile in the presence of a strong acid, and then neutralizing the effluent with ammonia, an amine or the like.

The method for producing this primary amine reacts a precursor compound for carbenium ion, shown by formula I or II (R1, R2, R3, R4 and R5 are each H, an alkyl, cycloalkyl or the like; and X is H, OH, a halogen, COOR and OCOR where R is alkyl or aryl) or the like with a nitrile mixed with a strong acid and water to form a solution at -20 to 80°C for 1 to 10h, where the mixed solution is added to the reaction system to have the strong acid/precursor molar ratio at (1.2-1.6):1, adds water to hydrolyze an excess nitrile, and neutralizes the effluent at 20 to 50°C with ammonia or the like, to produce the objective product shown by formula III separated in the organic phase. It is extracted, as necessary, with an adequate organic solvent.