To obtain with good productivity a film excellent in optical isotropy.

The film is manufactured by melting/extruding/casting a resin composition to form a film and then drawing it to at least either direction. The constituents of the resin composition used in that case are a maleimide-olefin copolymer of 65-75 wt% and an acrylonitrile-styrene copolymer of 35-25 wt%. The maleimide-olefin copolymer consists of 40-60 mole% of the component of structural formula (I) and 60-40 mole% of the component of structural formula (II) and has a number average mol. wt. of ≥1×103 and ≤5×106. The acrylonitrile-styrene copolymer contains the acrylonitrile unit of 21-45 wt%. The maximum phase difference of the film planar direction at the wavelength of 550 nm is <10 nm. In the structural formulas, R1 indicates a hydrogen or a 1-6C alkyl group, and R2 and R3 indicate each a hydrogen or a 1-6C alkyl group.