To provide a fuel cell system capable of suppressing drop in CO resistance of a catalyst of a fuel electrode in the power generation stop and storage of the fuel cell system.

A first cutoff valve 24 is installed in fuel gas supply piping 22 for supplying reformed gas to the fuel electrode 10a of a fuel cell 10, and a second cutoff valve 25 is installed in fuel gas exhaust piping 23. A CO adsorbent 40 is installed inside a fuel electrode outlet manifold 27. As the CO adsorbent 40, a substance having a higher CO adsorbing energy than a catalyst used in the fuel electrode 10a of the fuel cell 10 is used. The opening and closing of the first cutoff valve 24 and the second cutoff valve 25 are controlled with a control device 60, and in the power generation stop and storage of the fuel cell system, the control device 60 controls the first cutoff valve 24 and the second cutoff valve 25 to be closed.