Each battery module of a battery pack includes a stack of serially connected battery cells, a gas discharge duct extending in a cell arrangement direction to guide gas discharged from a relief valve of each battery cell to an outside of the battery module, the gas discharge duct having a first connection opening at one end and a second connection opening at the other end, a first connection terminal piece having an inner end portion electrically connected to an electrode of one of the battery cells at one end of the serial connection and an outer end portion disposed inside the first connection opening, and a second connection terminal piece having an inner end portion electrically connected to an electrode of another one of the battery cells at another end of the serial connection and an outer end portion disposed inside the second connection opening.