A fuel cell system includes a stack having an electricity generator for receiving fuel and air to generate electrical energy, a fuel supply unit for supplying the fuel to the stack, a housing in which the stack is mounted, a fan unit for supplying external air to the interior of the housing for cooling the electricity generator, and a region wherein air heated while cooling the electricity generator and air discharged from the stack and containing moisture are mixed. The air that is mixed in the region is discharged from the region.