Abstract: Dope is cast onto a casting drum to form a casting film. The casting film is cooled on the casting drum to be hardened. The casting film containing a large amount of solvent is peeled as a film from the casting drum. The film is dried in a tenter. Concretely, the film is dried until the residual amount of solvent becomes 60 mass %. Thereafter, the film is further dried by blowing gas at a temperature of at most 105° C. toward the film until the residual amount of solvent becomes 10 mass %. A glass transition temperature of cellulose acylate in the film in which a residual amount of solvent is 10 mass % is denoted by Tg (° C.). The film is subjected to a width increasing process while the temperature of the film is within a range between Tg+10° C. or more and Tg+60° C. or less to obtain a retardation film.