To provide a metal-clad substrate which scarcely has the partial irregularity of relative dielectric constant and dielectric loss tangent and has a high adhesive force between the metal foil and the substrate and whose surface is smooth in a state free from fine evenness.

This fluororesin fiber sheet comprising at least two kinds of fluroresin fibers A and B having different melting points, respectively, and heat-resistant insulating fibers is characterized in that the melting point MpA of the fluroresin fibers A and the MpB of the fluroresin fibers B satisfy the following expression (1): MpA-MpB>0 (1).