PURPOSE: To prevent a gap from being generated, eliminate the dispersion of the electrostatic capacity value, and prevent a corona discharge by molding two portions of insulating resin to an electrode at different temperatures.

CONSTITUTION: Insulating resin 6 is molded in a bottomed cylinder shape around a high-potential electrode 2. After it is cooled to 120°C, an outer ground potential electrode 3 is closely coupled around this insulating resin 6. Insulating resin 7 is integrally molded around this ground potential electrode 3 at 270°C. The shrinkage of insulating resin is large at the time of high-temperature molding, and a gap is apt to be generated, but two portions of the insulating resin have a temperature difference, thus insulating resin is filled, and no gap is generated.