A process by which many kinds of unstretched films comprising a thermoplastic resin are produced each in a small amount and high yield. A thermoplastic resin (A) to be formed into an unstretched film and another thermoplastic resin (B) are separately melted by heating. The thermoplastic resin (B) is introduced to each edge part of a T-die (2) for extrusion. The two resins are ejected and extruded on a casting roll so that the thermoplastic rosin (B) is disposed on the side of each edge of the thermally melted thermoplastic resin (A). Thus, an unstretched film (20) is formed which comprises the thermoplastic resin (A) and the thermoplastic resin (B) disposed on the side of each edge of the resin (A). Thereafter, the parts constituted of the thermoplastic resin (B) are removed y cutting to form a target unstretched film (20) consisting only of the thermoplastic resin (A).