To obtain a film having high optical characteristics by suppressing the occurrence of residual strain due to a polishing roller method and preventing the occurrence of fluctuations in thickness or streak trouble.

In this manufacturing method of a thermoplastic film 12 by melting a thermoplastic resin to extrude the same into a sheetlike form with a surface having an arithmetic average height Ra of at most 100 nm from a die 24 and holding the extruded sheet by a pair of rolls 26 and 28 at least one of which is constituted of an elastic roll 26 made of a metal to cool and solidify the same to form a film, the die clearance (d) of the die 24 is set to 0.2-1.0 mm and the resin flow rate per a unit area at a die extrusion port 24C is set to 0.1-1.5 kg/mm2per one hr.

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