To obtain a process for producing a phase difference film, with which the unequal phase difference within an intra-surface directing is lessened by using an extrusion deposition method.

A thermoplastic resin film is obtained by extrusion deposition a thermoplastic resin composition containing a thermoplastic resin and a plasticizer. Part of the plasticizer in this thermoplastic resin film is vaporized in at least one stage after the extrusion stage. This process for producing the phase difference plate film consists in uniaxially or biaxially stretching the thermoplastic resin film, while cooling the thermoplastic resin film kept at a specified temperature within the range of Tg-30°C to Tg+100°C, when the glass transition temperature of the thermoplastic resin is defined as Tg, at temperature lower than this specified temp.