To provide a method for manufacturing a polymer film with a visibility angle magnification effect which is free from rupture and surface defects during tenter stretching and also a trimming failure, and shows imparted appropriate retardation characteristics, and also to provide a phase differential film.

In the method for manufacturing a polymer film by which a dope containing a polymer and an organic solvent is cast over a support, then the organic solvent is evaporated and a cast film is stretched in the crosswise direction while gripping both end parts of the film using a gripper after the cast film is released from the support, the cast film is gripped after the temperature of the gripper is previously adjusted to be not lower than the boiling point of the organic solvent and less than the stretching temperature.

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