To prevent fouling from adhering on the surface of a support while producing a film.

A dope 70 is made using a cellulose acylate originated from a conifer. In the cellulose acylate, the molar equivalent of a compound contained in the cellulose acylate or of a bonded carboxylic acid group to the cellulose acylate is within the range of 3-15, the mass concentration of a Ca constituent in the cellulose acylate is 0-5 ppm, and the mass concentration of a Mg constituent is 10-70 ppm. A gel-like casted film 40 is formed by casting the dope 70 on an endlessly-running casting drum 34 having a cooled surface. A cleaning gas containing dry ice particles is blown on the surface of the casting drum 34 from a drum cleaning device 44. A film 51 is obtained by peeling the casted film 40 from the casting drum 34, and thereafter drying. The adhesion of fouling can be prevented by suppressing generation of a fatty acid Ca and the like, and by cleaning the surface of the casting drum 34 with the cleaning gas.