Fuel Cell System And Method For Operating Fuel Cell System

The present invention provides a fuel cell system which is capable of appropriately removing nonionic sulfur compound contained in recovered water in a water recovery device, which is used for generating a hydrogen-containing gas in a hydrogen generator, and a method for operating the fuel cell system. The fuel cell system ( 100 ) is comprised of: a hydrogen generator ( 1 ) configured to generate a hydrogen-containing gas from a feed gas and steam; a fuel cell ( 5 ) configured to generate electric power using the hydrogen-containing gas and an oxidizing gas; a water recovery device ( 12 ) configured to recover water generated through the electric power generation; a first water cleaning device ( 18 ) including an ion exchanger for removing ionic impurities contained in the water recovered by the water recovery device; a second water cleaning device ( 17 ) configured to remove a nonionic sulfur compound contained in the water recovered by the water recovery device, by chemical adsorption; and a water supply passage ( 40 ) configured to guide, to the hydrogen generator, the water which has been taken out of the water recovery device ( 12 ) and has flowed through the first and second water cleaning devices ( 18, 17 ).