In a flexible circuit board, signal wirings and ground wirings are provided on one main surface of a base film formed of a thermoset resin. A coverlay film formed of a thermoplastic resin is adhered to and integrated with the signal wirings, ground wirings, and base film. External terminals 15 are disposed in a predetermined conductor pattern on one main surface of the coverlay film, and a plated layer is formed on each of the external terminals. A first ground layer and a rear side resin film are adhered in this order below the base film to be integrated.