Dielectric circuit components such as a dielectric strip, dielectric blocks and dielectric ring inserted between conductive plates are molded from a thermoplastic material. As the thermoplastic material, thermoplastic resin is used which has a dielectric constant not greater than 2.4. The dielectric circuit components may be injection-molded from an injection-moldable high polymer material which contains fluorine and has a melting point not greater than 300.degree. C.