A solid oxide fuel cell system comprising: a reformer configured to generate a hydrogen-containing gas by using a raw material and water or humidified air; a solid oxide fuel cell including an anode and a cathode, and configured to generate electric power by using the hydrogen-containing gas supplied from the reformer to the anode and air supplied to the cathode; a heat radiator (17, 18) configured to radiate heat from at least one of an anode off-gas discharged from the anode and a combustion exhaust gas generated by combusting the anode off-gas to generate condensed water; a condensed water circulating passage configured to circulate the condensed water supplied from the heat radiator (17, 18); a condensed water tank provided on the condensed water circulating passage and configured to store the condensed water therein; a condensed water pump provided on the condensed water circulating passage and configured to circulate the condensed water; a condensed water/off-gas heat exchanger provided on the condensed water circulating passage and configured to exchange heat between the condensed water and an off-gas discharged from the solid oxide fuel cell to heat the condensed water by the off-gas; and a reforming water pump configured to supply to the reformer the condensed water as at least a part of the water supplied to the reformer; or a humidifier provided on the condensed water circulating passage and configured to humidify air using the condensed water to generate the humidified air supplied to the reformer, characterized in that the condensed water pump circulates the condensed water in such a manner that the condensed water discharged from the condensed water pump flows through the condensed water/off-gas heat exchanger, and wherein the condensed water/off-gas heat exchanger is a plate heat exchanger or a double-pipe heat exchanger. a reformer configured to generate a hydrogen-containing gas by using a raw material and water or humidified air; a solid oxide fuel cell including an anode and a cathode, and configured to generate electric power by using the hydrogen-containing gas supplied from the reformer to the anode and air supplied to the cathode; a heat radiator (17, 18) configured to radiate heat from at least one of an anode off-gas discharged from the anode and a combustion exhaust gas generated by combusting the anode off-gas to generate condensed water; a condensed water circulating passage configured to circulate the condensed water supplied from the heat radiator (17, 18); a condensed water tank provided on the condensed water circulating passage and configured to store the condensed water therein; a condensed water pump provided on the condensed water circulating passage and configured to circulate the condensed water; a condensed water/off-gas heat exchanger provided on the condensed water circulating passage and configured to exchange heat between the condensed water and an off-gas discharged from the solid oxide fuel cell to heat the condensed water by the off-gas; and a reforming water pump configured to supply to the reformer the condensed water as at least a part of the water supplied to the reformer; or a humidifier provided on the condensed water circulating passage and configured to humidify air using the condensed water to generate the humidified air supplied to the reformer, characterized in that the condensed water pump circulates the condensed water in such a manner that the condensed water discharged from the condensed water pump flows through the condensed water/off-gas heat exchanger, and wherein the condensed water/off-gas heat exchanger is a plate heat exchanger or a double-pipe heat exchanger.