Disclosed herein are an ionic conductor including a proton conductor, a process for production thereof, and an electrochemical device (such as fuel cell) with said ionic conductor, said ionic conductor being superior in ionic conductivity, water resistance, and film forming properties. The ionic conductor is formed from a polymer in which carbon clusters having ion dissociating functional groups are bonded to each other through connecting groups. The polymer is less water-soluble and more chemically stable than a derivative composed solely of carbon clusters; therefore, it permits many ion dissociating functional group to be introduced thereinto. Moreover, if ion dissociating functional groups are introduced into also the connecting group, it is possible to prevent the concentration of ion dissociating functional groups from decreasing as the result of polymerization. The polymer can be easily synthesized by simple condensation, substitution, and hydrolysis. Therefore, the process is suitable for mass production in high yields.