A fuel cell comprising a container and a fuel cell element or elements contained in the container, to which a mixed fuel gas containing a fuel gas and oxygen is fed to generate electricity, and the gas having passed through the fuel cell element or elements is discharged, as an exhaust gas, from the container, wherein the space other than the fuel cell element or elements in the container, through which the mixed fuel gas or the exhaust gas flows, is filled with packing materials to form a packed layer having a gap between the adjacent packing materials, at which gap the mixed fuel gas cannot be ignited, during the operation of the fuel cell, even if the mixed fuel gas has a fuel gas concentration within the ignition limits for the mixed fuel gas, and a burn-up section, in which the exhaust gas discharged from the packed layer is burned, is provided at, or in the vicinity of, the exhaust gas outlet of the container.