A method for producing a broadband wavelength film including, in this order: a first step of preparing a layer (A) as a long-length obliquely stretched film; a second step of forming on the layer (A) a layer (B) of a resin having a negative intrinsic birefringence to obtain a multilayer film; and a third step of stretching the multilayer film to obtain a long-length broadband wavelength film including a λ/2 layer and a λ/4 layer.