A high-reliability battery pack is described. A battery pack has a battery module unit that is formed from a plurality of arranged battery modules, each of which has a plurality of cells in a case, a cooling air flow passage where a cooling air flow flows, and a gas exhaust duct which forms a gas exhaust passage. The gas exhaust duct extends in an arrangement direction S of the plurality of the battery modules while being contiguous to the battery module unit, and takes in the gas released in the case from the cell, then exhausts the gas from the battery module. The gas exhaust duct is provided with a gas inlet for taking in the gas, which communicates with a gas emission hole formed on a surface of the case, and an air intake that serves to take in the cooling air flow.