To raise temperature of a fuel cell while avoiding partial damages or the like due to temperature changes with effective use of heat of exhaust gas exhausted from a cathode, and prevent carbon deposition at an anode.

The fuel cell system is provided with a fuel cell 10 generating power by making hydrogen-containing gas and oxygen-containing gas flow in contact with each other in an anode 12 and a cathode 13, and a first combustor 20 for combusting and heating fuel and the oxygen-containing gas to generate heating gas to be sent to the cathode 13. It heats and raises temperature of the fuel cell 10 before its start of operation so that the fuel cell 10 reaches an operable temperature by the heating gas. A first exhaust heated gas return path 17 is arranged for mixing part of exhaust heated gas exhausted from the cathode 13 with heating gas sent out from the first combustor 20 and returning and feeding it to the cathode 13, and, to the exhaust heated gas returning path 17, a gas feeder 50 is fitted for feeding exhaust heated gas.