A spacer disposed between first and second unit cells has a corrugated portion. The corrugated portion includes first and second protrusions alternating continuously and repeatedly in a vertical direction. The first protrusions protrude from a center in the thickness direction toward the first unit cell to form clearances that function as cooling passages between the first protrusion and the second unit cell. The second protrusions protrude from the center in the thickness direction toward the second unit cell to form clearances that function as cooling passages between the second protrusions and the first unit cell. The spacer includes a straight portion extending in a direction crossing the cooling passages so as to prevent elongation of the corrugated portion in a direction perpendicular to the cooling passages.