[Problem] To provide: a transparent film for a flexible circuit board, which is excellent in heat resistance and is suitable to form a circuit having a thinner wire; and a flexible circuit board. [Solution] A transparent film for a flexible circuit board characterized by including, on at least one surface of a polyester film, an undercoat layer made of a cured material containing an ultraviolet-curable resin composition, wherein the undercoat layer has a surface free energy of 20-40 mJ/m2, a surface roughness Ra of at most 10 nm, and a film thickness of 0.8-3.0 μm. A flexible circuit board wherein a circuit having a wire width of at most 30 μm is formed on the transparent film for the flexible circuit board.
