Method of fabricating substrate film

The present invention provides a substrate that is suitable for obtaining such a laminated member, and can be used to obtain a laminated member having a functional layer on a thin resin film while considering the operability and suppressing the influence on the quality of the functional layer in the manufacturing process. Manufacturing method of thin film. The invention is a method for manufacturing a base film, which is a method for manufacturing a long base film having a polyimide layer on a supporting material and forming a functional layer on the polyimide layer, which is characterized in that: The support material has a heat-resistant polyimide surface having a glass transition temperature of 300 ° C or more on the surface, and a polyamic acid resin solution is applied to the heat-resistant polyimide surface, and heat treatment is performed to make the polyamic acid The imidization forms a polyimide layer having a transmittance of 70% or more in a wavelength region of 440 nm to 780 nm on the heat-resistant polyimide surface.