At an optional stage in the production step of a biaxially stretched film using a polyamide resin including, as a first component, nylon 6, and as a second component, a polyamide including xylylenediamine and an aliphatic dicarboxylic acid having 4 to 12 carbon atoms, the film is brought into contact with water set at 40° C. or higher and lower than 70° C. for 1 to 10 minutes and further with water set at 70° C. or higher for 1 to 10 minutes. In the film thus obtained, the content of low molecular weight compounds is 0% by mass to 0.2% by mass.