A battery pack includes: at least one battery module; a housing; and attachment members. The at least one battery module is housed in the housing. The attachment members are coupled to the housing, and attachable to a vehicle body. The housing is positioned under a floor of a vehicle. Each of the attachment members extends from a side of the housing to another side along a lower surface of the housing. Lower surfaces of the attachment members are coupled to a plate member. A lower portion of the battery pack has a double-bottomed part formed by the plate member and a bottom surface of the housing.