A battery pack comprising: a pack case; and a plurality of battery modules arranged in the pack case, wherein each of the battery modules includes a plurality of cells arranged in a module case, each of the battery modules is separated into a battery chamber in which the plurality of cells are accommodated and an exhaust path through which an exhaust gas from at least one of the cells is released via an outlet opening to an outside of the battery module, one of the battery module is mounted on a module mounting member, the module mounting member is fixed to the pack case, the module mounting member is provided with an exhaust duct through which the exhaust gas released from the exhaust path passes, the module mounting member is disposed between the one of the battery module and a bottom surface of the pack case, the outlet opening is formed in a side surface of the module case, the plurality of battery modules are arranged in a direction to which the outlet opening is open, a side surface of the module case opposite to the side surface of the module case in which the outlet opening is formed is provided with an inlet opening to which the exhaust gas released from the outlet opening of an adjacent battery module is introduced, characterized in that the outlet opening is connected to the inlet opening of the adjacent battery module through a hollow connecting member (57, 253), a duct lower member forming the exhaust duct is in pressure contact with the bottom surface of the pack case, the module case is separated into the battery chamber and the exhaust path by the partition plate, the partition plate includes a plurality of through holes each exhausting gas of the plurality of the cells accommodated in the battery chamber, the exhaust path includes first exhaust path branches extending in the arrangement direction of the cells and allowing gas exhausted from the cells to flow, and a second exhaust path branch extending in a direction perpendicular to the arrangement direction of the cells, communicating with the first exhaust path branches, and allowing the gas from the first exhaust path branches to flow, and the outlet opening connected with the exhaust path of the downstream side battery module is formed at a longitudinal end of the second exhaust path branch. a pack case; and a plurality of battery modules arranged in the pack case, wherein each of the battery modules includes a plurality of cells arranged in a module case, each of the battery modules is separated into a battery chamber in which the plurality of cells are accommodated and an exhaust path through which an exhaust gas from at least one of the cells is released via an outlet opening to an outside of the battery module, one of the battery module is mounted on a module mounting member, the module mounting member is fixed to the pack case, the module mounting member is provided with an exhaust duct through which the exhaust gas released from the exhaust path passes, the module mounting member is disposed between the one of the battery module and a bottom surface of the pack case, the outlet opening is formed in a side surface of the module case, the plurality of battery modules are arranged in a direction to which the outlet opening is open, a side surface of the module case opposite to the side surface of the module case in which the outlet opening is formed is provided with an inlet opening to which the exhaust gas released from the outlet opening of an adjacent battery module is introduced, characterized in that the outlet opening is connected to the inlet opening of the adjacent battery module through a hollow connecting member (57, 253), a duct lower member forming the exhaust duct is in pressure contact with the bottom surface of the pack case, the module case is separated into the battery chamber and the exhaust path by the partition plate, the partition plate includes a plurality of through holes each exhausting gas of the plurality of the cells accommodated in the battery chamber, the exhaust path includes first exhaust path branches extending in the arrangement direction of the cells and allowing gas exhausted from the cells to flow, and a second exhaust path branch extending in a direction perpendicular to the arrangement direction of the cells, communicating with the first exhaust path branches, and allowing the gas from the first exhaust path branches to flow, and the outlet opening connected with the exhaust path of the downstream side battery module is formed at a longitudinal end of the second exhaust path branch.