A battery pack includes: a housing; a battery stack being housed in the housing, the battery stack including a plurality of prismatic batteries stacked on each other in a row; a one-side restraint portion that restrains one side of the battery stack in a Y direction; an opposite-side restraint portion that restrains another side of the battery stack in the Y direction; a housing-side end plate that restrains one side in the X direction of the battery stack and oppositely faces a housing inner-surface in the X direction; and a plate movement allowing and positioning mechanism that allows movement of the housing-side end plate in the X direction due to the expansion of the battery stack in the X direction, and positions the housing-side end plate with respect to housing 2 in the Y direction.