To provide a method for producing the subject compound, as an important intermediate for medicines, aprochemicals, liquid crystals, monomers for functional polymers or the like, industrially advantageously in high yield and high purity, by reacting a benzamide compound containing a specific cyano group with a nitrogen oxide.

This method comprises reacting a benzamide compound containing cyano group, shown by formula I [CONH2 is m- or p-site of CN; X is Cl or F; and (n) is 0 to 4], e.g. m- or p-cyanobenzamide with a nitrogen oxide (NO, N2O3, NO2, N2O4 or N2O5), to produce the target compound shown by formula II (COOH is m- or p-site of CN), e.g. m- or p-cyanobenzoic acid. It is preferable that the above reaction is effected in an organic solvent (e.g. polar organic solvent, in particular a mixed solvent of carboxylic acid and carboxylic acid anhydride) in the presence of a base (e.g. carboxylate) in an acidic aqueous solution.