To provide a method for screening a processing agent having excellent economical efficiency, large functionality-imparting effects, excellent durability and high practical values and to provide a method for processing by paying attention to points at issue that improving processing of moisture retaining properties of nylon easily causes problems in feeling with insufficient durability of processing effects and a plurality of kinds of processing agents are expensive causing problems in economical efficiency with difficulty in obtaining reproducibility in quality of processed products etc.

The method for producing a modified polyamide-based fiber material uses a polyfunctional type cationizing agent as a binder for animal and vegetable proteins and reacting a polyamide-based fiber material with the animal and vegetable proteins in water solvent.