There are provided a solid oxide fuel cell system made up of (a) a solid
oxide fuel cell stack, (b) a preliminary reformer for removing
hydrocarbons having two or more carbon atoms from a hydrocarbon fuel by
converting the hydrocarbons having two or more carbon atoms into methane,
hydrogen, and carbon monoxide, and (c) an integrated heat exchanger for
catalytic combustion for heating either air or fuel, or both the air and
fuel, to be guided to the solid oxide fuel cell stack, by use of a
combustion gas formed by combusting discharged fuel with the use of
discharged air, wherein the component equipment described above are
disposed in an adiabatic vessel and the integrated heat exchanger for
catalytic combustion for use in the solid oxide fuel cell system.