The case 20 housing a plurality of cells 100 is divided, by a circuit board 30 provided at the same sides of the cells 100, into a housing space 50 housing the cells 100 and an exhaust duct 60 for releasing a gas from the vents 8a of the cells 100 to outside the case 20. The vents 8a of the cells 100 communicate with the exhaust duct 60 through openings 30a formed in the flat plate 30. The exhaust duct 60 is divided into a first space 61 and a second space 62 by a partition 40 provided between the flat plate 30 and an external plate 21 of the case 20. The first space 61 communicates with the second space 62 through through holes 40a formed in the partition 40.