Solid polymer electrolyte fuel cell assembly, fuel cell stack, and method of operating cell assembly

A cell assembly (10) is formed by stacking a first unit cell (14) and a second unit cell (16) to each other. The first unit cell (14) includes a first unified body (18), and the second unit cell (16) includes a second unified body (20). In the cell assembly (10), the first and second unit cells (14, 16) have structures different from each other.