To obtain a resin film capable of forming a hydrophilic group or water-repellent group onto film surface and imparting antifogging properties to the film surface and useful for agricultural film by carrying out discharge plasma treatment of a thermoplastic resin film in the mixture of a gas for treatment with an inert gas.

A solid dielectric is installed on at least one opposed face of opposed electrodes and a thermoplastic resin film is installed between the electrode and the solid dielectric or between opposed faces of these solid dielectrics, and the surface of the film is subjected to discharge plasma treatment under a pressure close to atmospheric pressure of a mixed gas of a gas for treatment with an inert gas. Furthermore, a fluorocarbon group is preferably introduced onto the surface of the film by using a fluorine-containing gas (e.g. tetrafluorocarbon) as the gas for treatment to impart water repellency to the film surface.