Disclosed herein are an ion-dissociative functional compound, a method for production thereof, an ionic conductor, and an electrochemical device, the ion-dissociative functional compound being thermally and chemically stable under the condition required of fuel cells and being suitable for use as a material such as protonic conductor in fuel cells.The proton-dissociative functional compound shown in FIG. 1A is composed of a fullerene C60 molecule and about 10 sulfonic acid groups —SO3H as proton-dissociative groups each attached to the fullerene through a difluoromethane group —CF2—. The proton-dissociative functional compound shown in FIG. 1B is composed of fullerene molecules three-dimensionally connected to each other through a linking group —CF2SO2NHSO2CF2—. It contains, as the proton-dissociative group, sulfoneimide groups —SO2NHSO2— and sulfoneamide groups —SO2H2 in addition to sulfonic acid groups. These compounds are prepared by introduction of difluoro(fluorosulfonyl)methyl groups into fullerene molecules, and ensuing imidization and hydrolysis.