PROBLEM TO BE SOLVED: To provide a solid oxide electrochemical cell stack structure improved in heat exchange efficiency and also capable of suppressing breakage of a sealing material provided on a side surface portion thereof.SOLUTION: A solid oxide electrochemical cell stack structure includes a plurality of cell stacks and a flat plate-like heat exchanger disposed between the cell stacks. In each of the cell stacks, a plurality of flat plate-like solid oxide electrochemical cells are stacked.