NOVELTY - Fuel cell electric power generating system has modifiers (52,53), fuel cell stacks (9,38), carbon monoxide selective oxidation device (5) and shift converter (4) for producing carbon dioxide and hydrogen. Modifier (52) generates hydrogen-rich reformed gas. Modifier (53) has burner (54) for producing gas of reduced methane concentration. Stack (9) produces power by reacting oxygen and hydrogen contained in exhaust gas of device (5).    USE - For generating electric power.    ADVANTAGE - The system efficiently enables the generation of electric power, using fuel cell stack operating at low temperature.    DETAILED DESCRIPTION - The fuel cell electric power generating system has modifiers (52,53), fuel cell stacks (9,38), carbon monoxide shift converter (4) and carbon monoxide selective oxidation device (5). The modifier (52) generates hydrogen-rich reformed gas by water vapor modification reaction of fuel. The modifier (53) has a modifier burner (54), which produces hydrogen-rich reformed gas of reduced methane concentration by carrying out water vapor modification of methane in reformed gas. Carbon monoxide, oxygen, and hydrogen, or hydrogen contained in hydrogen-rich reformed gas, are reacted to produce electric power. Exhaust heat and water vapor-containing exhaust gas produced during electric power generation are supplied to modifier (52), by fuel cell stack (38). The converter (4) carries out reaction of water vapor and carbon monoxide contained in methane concentration-reduced hydrogen-rich reformed gas, and produces carbon dioxide and hydrogen. The device (5) carries out oxidation of carbon monoxide contained in exhaust gas of converter (4) using oxygen, and produces carbon dioxide. The fuel cell stack (9) carries out electrochemical reaction of oxygen and hydrogen contained in exhaust gas of device (5), and produces electric power.    DESCRIPTION OF DRAWING(S) - The figure shows the structure of fuel cell electric power generating system. (Drawing includes non-English language text).    Carbon monoxide shift converter (4)    Carbon monoxide selective oxidation device (5)    Modifiers (52,53)    Modifier burner (54)    Fuel electrode (35)    Fuel cell stacks (9,38)