A cell assembly includes a first unit cell and a second unit cell which are stacked to each other. The first unit cell has a first unified body, and the second unit cell has a second unified body. A plurality of oxidizing gas passages and a plurality of fuel gas passages are provided in the cell assembly. The oxidizing gas passages in the first unit cell and the oxidizing gas passages in the second unit cell are communicated in series to each other. The fuel gas passages in the first unit cell and the fuel gas passages in the second unit cell are communicated in series to each other.