Resin film, method for producing resin film, and method for producing retardation film

Provided are: a resin film which has an excellent appearance and can be suitably used in the production of a retardation film having reverse wavelength dispersion characteristics; a method for producing the resin film; and a method for producing a retardation film using the resin film. A resin film according to an embodiment of the present invention contains a resin exhibiting positive birefringence and a resin exhibiting negative birefringence, and the difference in refractive index between one surface and the other surface satisfies formula (I). The refractive index difference < = the thickness of the resin film * 0.00001 (I). 本发明提供一种具有优异的外观、能够适合用于具有逆波长分散特性的相位差膜的制造的树脂膜及其制造方法、和使用了该树脂膜的相位差膜的制造方法。本发明的实施方式的树脂膜含有显示正的双折射的树脂和显示负的双折射的树脂，并且一个面与另一个面的折射率差满足下述式(I)。该折射率差≤|树脂膜的厚度×0.00001|(I)。