There is provided a method for thermochemically producing hydrogen from water by using sulfuric acid as a kind of reactant, combining a plurality of chemical reactions inclusive of sulfuric acid decomposition reaction and circulating reactants. The sulfuric acid decomposition reaction is carried out at a temperature of 600.degree. C. or less by electrolysis using a partition wall of oxygen ion-permeable solid electrolyte and oxygen is separated simultaneously with the electrolysis to thereby carry out the method for producing hydrogen by chemical process using heat with electricity.