Battery pack

In a battery pack where a fan is housed within a case housing a battery stack, the noise generated from turbulence of a medium that is supplied and exhausted between a fan opening of the fan and the battery stack is reduced. The battery pack has a battery stack, a cooling fan installed adjacent to the battery stack and having a fan opening formed in a top surface for taking in cooling air after cooling the battery stack, an upper case for covering the upper part of the battery stack and the cooling fan, and a junction duct for guiding the cooling air after cooling the battery stack to the fan opening. The junction duct is formed from the duct lower unit having an opening formed at a location facing the fan opening and one wall of the upper case in contact with a lower end and periphery of the duct lower unit.