A circuit substrate having an insulating layer comprising a polyimide resin on a metal foil substrate, wherein the polyimide resin is a polyimide resin obtained by the reaction of (A) aromatic diamines comprising (a) p-phenylene diamine and (b) 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl. (B) 3,4,3',4'-biphenyltetracarboxylic acid dianhydride. The circuit-formed substrate has a desired circuit comprising a conductive layer on the circuit substrate. The polyimide resin has a coefficient of thermal linear expansion close to that of the metal foil, and hence breakage does not occur on the resin layer, the resin layer does not separate, and warping does not occur.