To prevent stain adhesion to the surface of a support.

A dope 70 containing a cellulose acylate and a solvent is prepared. The cellulose acylate is produced from wood as a raw material. The molar equivalent of a compound or a bonded carboxylic acid group contained in the cellulose acylate in relation to the cellulose acylate is 3-15. The mass concentration of a Ca component is 0-5 ppm, and the mass concentration of an Mg component is 20-60 ppm. The dope 70 is cast on an endlessly traveling casting drum 34 with its surface cooled to form a gelatinous cast film 40. After that, the cast film 40 is stripped off from the casting drum 34 and dried to obtain a film 51. The surface of the casting drum 34 is irradiated with laser beams from a drum washing machine 44. Organic substances on the casting drum 34 are decomposed/removed. In this way, since the production of a fatty acid calcium etc., which can be stain is suppressed, stain adhesion to the casting drum 34 can be prevented.