A fuel cell cassette, comprising: a single cell formed in a flat plate shape and having a fuel electrode, an air electrode and an electrolyte layer; a first frame formed in a frame shape and arranged to surround a peripheral surface of the single cell; a separator (12, 110) joined to a peripheral end portion of the single cell and located on one surface of the first frame so as to separate an oxidant gas contacting the air electrode and a fuel gas contacting the fuel electrode; and an interconnector formed in a plate shape and located on the other surface of the first frame opposite to the one surface on which the separator is located, wherein the fuel cell cassette comprises: a second frame (15, 112) located on the other surface of the separator opposite to the one surface on which the first frame is located, the second frame having defined therein gas channels (75, 76, 81, 82, 114) through which the oxidant gas or the fuel gas flows characterized in that the separator (12, 110) and the first frame are joined by welding such that the first frame is located on one surface of the separator, and welding parts (77, 83, 85 to 88) are formed on an exposed region of the separator (12, 110) inside the gas channel (75, 76, 81, 82, 114) so as to fix the exposed region of the separator (12, 110) to the first frame. a single cell formed in a flat plate shape and having a fuel electrode, an air electrode and an electrolyte layer; a first frame formed in a frame shape and arranged to surround a peripheral surface of the single cell; a separator (12, 110) joined to a peripheral end portion of the single cell and located on one surface of the first frame so as to separate an oxidant gas contacting the air electrode and a fuel gas contacting the fuel electrode; and an interconnector formed in a plate shape and located on the other surface of the first frame opposite to the one surface on which the separator is located, wherein the fuel cell cassette comprises: a second frame (15, 112) located on the other surface of the separator opposite to the one surface on which the first frame is located, the second frame having defined therein gas channels (75, 76, 81, 82, 114) through which the oxidant gas or the fuel gas flows characterized in that the separator (12, 110) and the first frame are joined by welding such that the first frame is located on one surface of the separator, and welding parts (77, 83, 85 to 88) are formed on an exposed region of the separator (12, 110) inside the gas channel (75, 76, 81, 82, 114) so as to fix the exposed region of the separator (12, 110) to the first frame. a second frame (15, 112) located on the other surface of the separator opposite to the one surface on which the first frame is located, the second frame having defined therein gas channels (75, 76, 81, 82, 114) through which the oxidant gas or the fuel gas flows characterized in that the separator (12, 110) and the first frame are joined by welding such that the first frame is located on one surface of the separator, and welding parts (77, 83, 85 to 88) are formed on an exposed region of the separator (12, 110) inside the gas channel (75, 76, 81, 82, 114) so as to fix the exposed region of the separator (12, 110) to the first frame.