A fuel cell system according to the present invention includes a cell stack, a combustion part, a reformed water carburetor, a gas mixer, and a reformer. The cell stack is a cell stack that is configured by stacking fuel cells and generates electric power by using hydrogen-containing gas and oxygen-containing gas. The combustion part burns the hydrogen-containing gas and the oxygen-containing gas that have not been consumed in the cell stack. A reformed water carburetor is communicated with the combustion part via an exhaust gas passage and generates steam. The gas mixer, placed on the top of the combustion part. The reformer, placed on the top of the combustion part in contact with the gas mixer, is a reformer, generates the hydrogen-containing gas by reforming the mixed gas, and supplies the hydrogen-containing gas to the cell stack via the hydrogen gas passage.