A fuel cell system includes a fuel cell module, auxiliary equipment, a power converter, and a casing containing the fuel cell module, the auxiliary equipment, and the power converter. The casing has a plurality of surfaces including one detachable maintenance surface. Only the maintenance surface has an air intake port for taking an oxygen-containing gas into the casing, an air exhaust port for discharging an exhaust gas discharged from the fuel cell module, to the outside of the casing, and a ventilation inlet port and a ventilation outlet port for ventilation of an inside of the casing by air.