Vehicle-mounted fuel cell stack includes one or more cooling cells and an air allocation mechanism. Via the allocation mechanism, air flowing in a front-to-rear direction of the vehicle is introduced through reacting-air introduction openings of power generating cells and also introduced through cooling-air introduction openings of the cooling cells, so that the power generating cells can be cooled by the cooling cells. Sliding movement of the air allocation mechanism can allocate the cooling air and reacting air in desired amounts, so that it is possible to not only appropriately deal with an increase in the power generation amount but also appropriately remove excessive heat. Because the cooling cells are each constructed of thin metal plates, they can effectively remove a great amount of heat produced from power generating cells, with an enhanced efficiency.