A process is provided for reforming a hydrocarbon with carbon dioxide using a selectively permeable membrane reactor including a catalyst for accelerating a chemical reaction and a selectively permeable membrane exhibiting selective permeability, wherein a carbon dioxide reforming reaction of the hydrocarbon is accelerated by the catalyst to produce reaction products, and a specific component among the reaction products is allowed to pass through the selectively permeable membrane so specific component is selectively separated. The process includes the steps of adding steam to a raw material gas containing the hydrocarbon and the carbon dioxide and supplying the raw material gas mixture to the selectively permeable membrane reactor.