A battery pack includes: a plurality of battery modules disposed adjacent to each other in a first direction inside a pack case, each of the plurality of battery modules including a plurality of battery cells disposed side by side in a second direction, the second direction being orthogonal to the first direction; and a side-frame disposed between the battery modules disposed adjacent to each other in the first direction inside the pack case. The side-frame includes two side-walls and a joint. The two side-walls elastically press side-surfaces, in the first direction, of the battery modules disposed adjacent to each other. The side-frame has a long-length shape with a U-shaped cross section. In a state where the side-frame is removed from the battery modules disposed adjacent to each other, a distance between the two side-walls of the side-frame becomes larger as the two side-walls go away toward opposite the joint.