The invention offers a high-frequency circuit substrate that sufficiently decreases the transmission delay and transFmission loss in comparison with the conventional high-frequency circuit substrate. In the offered high-frequency circuit substrate, a dielectric layer made of fluororesin is brought into intimate contact directly with a metal conductor that is used for wiring and that has a surface not subjected to coarsening treatment or primer treatment. The offered high-frequency circuit substrate causes a transmission loss of −3 dB/m or less at a frequency of 1 GHz and has a combined specific inductive capacity of 2.6 or less and a combined dielectric loss tangent of 0.0007 or less.