TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Method: Drying wind is applied to air surface at winding speed of 3-15 m/second, and skin layer is formed. The air surface is dried using a slit nozzle for taking drying wind from slit provided facing the air surface, and a chamber (69) having two-dimension nozzle which takes drying wind from primary opening provided facing air surface, and sucks air of spread film vicinity from secondary opening. The spread film is dried such that residual solvent amount is set to 150-500 wt.% by dry basis. The liquid contacting process is performed two or more times by immersing spread film and moisture film in the liquid.Preferred Liquid: The liquid contains one or more types of compounds.Preferred Solvent: The organic solvent is mixture of poor solvent of solid electrolyte, and good solvent. The weight proportion of poor solvent in organic solvent is 10-100%. The poor solvent contains 1-5C alcohol. The good solvent contains dimethyl sulfoxide.    TECHNOLOGY FOCUS - POLYMERS - Preferred Component: The solid electrolyte is a hydrocarbon group polymer. The hydrocarbon group polymer is an aromatic polymer having sulfonic acid group. The aromatic polymer is a copolymer containing structural units of formulae (I or II), or unit of formula: -(O-Z-O)-.X=hydrogen or monovalent cation group;Y'=SO2;Z=group of formula (a or b);andn/(m+n)=0.1-0.5. EXAMPLE - Sulfo propylated polyether sulfone having sulfonated degree of 35% (in wt.pts) (100) and N-methyl pyrrolidone (400) were mixed on dry basis, and solid electrolyte dope was produced. The obtained dope was flow-spread from spread die, and a spread film was formed. The film was dried by spraying wind of temperature 120degreesC. The spread film was peeled off, and further dried by spraying 100degreesC dry wind. Cutting removal of damaged portion of both ends of film was carried out. The film was then contacted with aqueous solution of methanol and dried at 140-160degreesC to produce solid electrolyte film. The film had thickness of 53 microns, dispersion in thickness of 52plus minus1.5 microns, residual solvent amount of 0.5 wt.%, and ion electrical conductivity of 0.1-0.11 S/cm. The electrolyte film provided fuel cell having power density of 0.49-0.51 W/cm2.