Solid polymer electrolyte fuel cell assembly, fuel cell stack, and method of supplying reaction gas in the fuel cell assembly

A cell assembly (10) includes a first unit cell (14) and a second unit cell (16) stacked 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), oxidizing gas passages (56) and (52) and fuel gas passages (46) and (58) are provided in parallel along the first and second unit cells (14) and (16).