from a quaternary ammonium compound a lower alkylamine and ammonia to preferably treat the used catalyst by using this aqueous solution on the same conditions as the contact treatment described above the used catalyst that is subjected to the adsorption treatment and the contact treatment may be fired previously under an oxygen containing gas atmosphere such as air so that the carbonaceous material precipitated on the catalyst may be burned and removed or may be subjected to the treatments of the present invention without being fired this firing may be performed in coexistence with an alcohol in accordance with the process proposed in jp 3 207454 a corresponding to ep 0388070 a1 for example the regenerated catalyst obtained in the above manner can be reused for the above mentioned beckmann rearrangement reaction of cyclohexanone oxime and such regeneration and reuse of the catalyst allows e caprolactam to be produced with high yield for a long period as described above in the case of performing the beckmann rearrangement reaction in combination with catalyst firing treatment the catalyst after this firing treatment is preferably subject to the adsorption treatment and the contact treatment for example as described above in the case where the reaction by supply of cyclohexanone oxime and the firing by supply of oxygen containing gas are repeated in a fixed bed reaction vessel filled with the catalyst the catalyst is preferred to be subject to the adsorption treatment and the contact treatment after the firing every time or at several time intervals and on this occasion the catalyst may be subject to the.