An optical fiber-containing insulator including an insulator body having a through hole and an optical fiber inserted into the through hole in which an insulation gas or an organic material is filled in a middle portion of the through hole, the insulator comprising wide-mouthed portions arranged in both end portions of the through hole, cylindrical members inserted into the wide-mouthed portions and heat-resistive adhesive agent member arranged between the insulation gas or organic insulation material and the cylindrical member. A process for producing such an optical fiber-containing insulator is also disclosed.