PURPOSE: To advantageously obtain the subject compound according to a continu ous method by specifying a feeding position of a raw material, etc., and a taking out position of a reaction product and reaction temperature, etc., in each reaction vessel, diazotizing an aromatic amine and then dediazotizing the resultant compound respectively in the presence of hydrogen fluoride.

CONSTITUTION: An aromatic amine is mixed with HF at -20 to +20°C tempera ture to form a solution 1 of anilinium fluoride in the hydrogen fluoride. The resultant solution is then cooled to -20 to +10°C and continuously fed to the bottom of the first reaction vessel 2 and an alkali nitrite is subsequently intro duced from the top thereof. Both are brought into contact in the reaction vessel 2 to afford an aryldiazonium fluoride. The obtained reaction mixture is further continuously taken from the top of the aforementioned reaction vessel 2, continu ously fed from the bottom into the second preferably tilted cylindrical reaction vessel 6 and thermally decomposed (dediazotized) at 40-150°C temperature. The resultant product is then partially passed through the top thereof and continuous ly taken out to facilitate temperature control of the reaction system and sup press side reaction. Thereby, the subject compound is continuously and readily obtained in high yield and purity.