A synthetic resin film which has a very uniform thickness, and a method of and an apparatus for uniforming the thickness of a synthetic resin film upon molding of the synthetic resin film wherein a plurality of heating means (5) are individually controlled rapidly in a required manner to obtain a synthetic resin film (3) of a uniform thickness. A thickness of a film molded by a die is measured by a film thickness measuring means (8), and measured values are taken into a calculating means. At the calculating means (7), a corresponding relationship is calculated, based on the measured film thickness values, between a one-sided material portion of the film and a plurality of heating means (5) adjacent a die lip of the die, and amounts of heat to be generated by the corresponding heating means (5) are controlled in accordance with amounts of one-sided material at the one sided material portion of the film.
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