The present invention relates to a preheating arrangement in a fuel cell apparatus, the fuel cell apparatus comprising at least a fuel cell unit, the fuel cells of which include an anode side and a cathode side and an electrolyte therebetween and in which fuel cell apparatus there is at least a fuel inlet into the anode side and an oxygen-containing gas inlet into the cathode side as well as a de-sulphuring unit and a fuel modifying unit and an afterburner for combusting the exhaust gases of the anode and/or cathode sides. According to the invention, a separate fuel channel has been arranged for the afterburner for introducing fuel to the afterburner at least during the start-up phase of the fuel cell apparatus and that at least a portion of the exhaust gases formed in the combustion of the separately fed fuel is arranged to be directed during the start-up phase of the fuel cell apparatus from the afterburner for heating at least the de-sulphuring unit and/or the fuel modifying unit.