A fuel cell system includes a reformer, a raw-material supplier, a desulfurizer, a flow controller, a vapor supplier, a fuel cell, a combustor, and a controller. After the raw-material supplier supplies a raw material at the startup of the fuel cell system, the controller causes the combustor to combust the raw material exhausted as off-gas from the fuel cell, subsequently causes the flow controller to allow gas exhausted from the reformer to flow through a recycle gas passage, and thereafter causes the vapor supplier to supply vapor, or the controller causes the flow controller to allow the gas exhausted from the reformer to flow through the recycle gas passage, subsequently causes the combustor to combust the raw material exhausted as the off-gas from the fuel cell, and thereafter causes the vapor supplier to supply the vapor.