A battery pack includes: energy storage devices arranged with a gap which is formed between the energy storage devices for passing a fluid; a case configured to accommodate the energy storage devices; a first duct disposed in an inside of the case and defining a supply flow passage through which the fluid is supplied to the gap; and a second duct disposed in the inside of the case and defining a discharge flow passage through which the fluid which has passed through the gap is discharged, wherein an auxiliary flow passage where the fluid flows along an outer surface of the first duct is formed, and the fluid is made to flow through the supply flow passage and the auxiliary flow passage at a same time.