A fuel cell device is provided and includes a plurality of cell units arranged in superposed layers and each comprising a cell having an anode formed on one surface of an electrode member and a cathode formed on the other surface of the electrode member, a fuel-side-plate having a fuel chamber for passing a fuel therethrough, and an oxidant-side-plate having an oxidant chamber for passing an oxidant gas therethrough, an oxidant supply channel for supplying the oxidant gas to the oxidant chamber and an oxidant discharge channel for releasing to the outside air an oxidant exhaust gas discharged from the oxidant chamber, the cell being sandwiched between the plates. The oxidant discharge channel has a first opening in communication with the oxidant chamber and a second opening in communication with the outside air, the second opening being smaller than the first opening in width.