NOVELTY - The fuel cell system (10) has control device (18) with partial oxidation reformer adjuster (90), combustion starter (92), and power generator (94). The partial oxidation reformer adjuster adjusts temperature of partial oxidation reformer (44), supply amount of raw fuel and supply amount of oxygen-containing gas, combustion starter starts combustion in exhaust gas combustor (46) and power generator starts power generation in fuel cell stack (22) based on at least any of reforming state in partial oxidation reformer, combustion state in exhaust gas combustor, and temperature of fuel cell stack.    USE - Fuel cell system for stationary and mobile applications such as vehicle.    ADVANTAGE - Facilitates thermally self-sustaining operation easily since partial oxidation reformer is adjusted to satisfy desired reforming conditions, and exhaust gas combustor is adjusted to satisfy combustion conditions for maintaining the self-ignition temperature, and fuel cell stack is adjusted to satisfy desired power generation conditions. The stability in starting operation is improved since partial oxidation reformer, exhaust gas combustor, and fuel cell stack achieve reduction in the time required for starting operation. Eliminates need to provide steam reformer since partial oxidation reformer is provided. The reduction in the number of parts is achieved, and reduction in the cost and size of entire fuel cell system is obtained since water supply system for supplying water vapor is omitted. The heat energy loss is suppressed, and thermally self-sustaining operation is facilitated easily since heat radiation from the fuel cell stack is minimized, and variation in the temperature distribution in the fuel cell stack is reduced.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic block diagram of the structure of a fuel cell system.    Fuel cell system (10)    Control device (18)    Fuel cell stack (22)    Partial oxidation reformer (44)    Exhaust gas combustor (46)    Partial oxidation reformer adjuster (90)    Combustion starter (92)    Power generator (94)