Noise generated from some air leaking from a water drain hole formed in an exhaust duct is reduced. A first water drain hole for exhausting liquid that has collected within the exhaust duct to outside the exhaust duct is formed in a bottom face of the exhaust duct for exhausting air after cooling a battery stack and a second water drain hole for exhausting liquid, which was exhausted from the first water drain hole, to outside a lower case is formed in the lower case housing the battery stack and the exhaust duct, with the second water drain hole formed at a position not on a line extending from the direction of outflow of air leaking out from the first water drain hole.