tribasic and the like of these catalysts it is preferable to use an alkali metal phosphate in terms of the reaction yield and it is further preferable to use tripotassium phosphate from the viewpoint of the economy of production in the present invention it is preferable that the total amount of these catalysts used be 0 1 to 50 by weight and particularly preferably 0 1 to 5 by weight relative to the weight of the aldoxime 2 which is a starting material compound in the present invention the reaction temperature for obtaining the nitrile 1 from the aldoxime 2 is 80 to 200 u00b0 c and preferably 100 to 160 u00b0 c in the present invention processes for distilling water which is produced with the progress of the reaction away from the reaction system are not particularly limited and highly efficient examples thereof include a process in which the water is removed by azeotropic distillation using a solvent which can be azeotropically distilled with water a process in which the water is distilled away by evaporation with the pressure in the reaction system being reduced and the like examples of the above described solvent which can be azeotropically distilled with water include benzene toluene xylene chlorobenzene heptane and the like in the present invention when the above described process in which the water is removed by azeotropic distillation using an azeotropic solvent is employed the reaction for obtaining the nitrile 1 from the aldoxime 2 is preferably conducted under atmospheric pressure in general on the other hand when the process in which a high boiling point solvent is added and the water is distilled away by evaporation under reduced pressure the reaction is conducted preferably at 200 torr or below.