A capacitor is formed between a lower wiring layer and an upper wiring layer in an interior of a circuit board. The capacitor is formed of a lower metallic layer which is of at least one valve metal selected from the group consisting of aluminum, tantalum, niobium, tungsten, vanadium, bismuth, titanium, zirconium and hafnium, a dielectric layer which is of an oxide of the valve metal which may be the same as or different from the valve metal of the lower metallic layer, an intermediate layer which is of a solid electrolyte, and an upper metallic layer which is of an electrode metal, laminated in this order.