A fuel gas inlet, a fuel gas outlet, an oxygen-containing gas inlet, an oxygen-containing gas outlet, and other components, which are disposed at upper and lower portions at both ends in the lateral direction, are provided in a first fuel cell stack. A plurality of cooling medium inlets, a plurality of cooling medium outlets, and other components are provided at lower portions on the long side and at upper portions on the long side respectively. A cooling medium flows from the lower portions to the upper portions through cooling medium flow passages to cool the power generation surface smoothly and reliably.