NOVELTY - Raw materials and mineral fuel (6) are modified in a polymer electrolyte fuel cell (9), to produce hydrogen-rich gas. The hydrogen-rich gas and oxygen are electrochemically reacted through a solid polymer electrolyte, to produce electricity. A sulfur compound is removed from the raw materials and mineral fuel by using a desulfurizing agent. When reformed gas is not recyclable, for example during starting, the recycle of reformed gas is stopped temporarily and desulfurization is carried out, and then recycle is started.    USE - Electric-power generation using polymer electrolyte fuel cell.    ADVANTAGE - The method achieves high degree of desulfurization which is stabilized using a small amount of desulfurizing agent, and is efficient and maintenance-free. Production of ammonia by condensation of water during recycle of reformed gas, is prevented.    DETAILED DESCRIPTION - Raw materials and mineral fuel are modified in a polymer electrolyte fuel cell, to produce hydrogen-rich gas. The hydrogen-rich gas and oxygen are electrochemically reacted through a solid polymer electrolyte, to produce electricity. A sulfur compound is removed from the raw materials and mineral fuel by using a desulfurizing agent. The desulfurized raw material and mineral fuel are reacted with sewage steam (7) of steam modification catalyst, to produce reformed gas. Carbon monoxide contained in the reformed gas is selectively oxidized using oxygen of air (8) in the presence of carbon-monoxide selective-oxidation catalyst, and converted into carbon dioxide. Before carbon-monoxide selective oxidation and addition of air for oxidation, condensation-separation of steam is carried out with respect to portion(s) of reformed gas by steam condensation-separation process. The condense-separated gas is recycled, and added to the raw materials and mineral fuel. Desulfurization is carried out using a hydrogenated adsorption desulfurizing agent containing copper, zinc, nickel and/or iron. When reformed gas is not recyclable, for example during starting, the recycle of reformed gas is stopped temporarily and desulfurization is carried out, and then recycle is started.    DESCRIPTION OF DRAWING(S) - The drawing shows a flowchart of the polymer electrolyte fuel cell electric-power generation system.    Modification reactor (2)    Raw materials and mineral fuel (6)    Steam (7)    Air (8)    Polymer electrolyte fuel cell (9)