To provide a battery pack capable of, even if an electrode area is large, easily applying a proper pressing pressure to a laminated body in which unit cells are laminated one on another. The battery pack has a laminated body 140 in which unit cells 10 are laminated one on another, a cell case 120 having a first opening 126 and containing the laminated body 140, and a first lid member 170 to tightly close the first opening 126. The first opening 126 is positioned to face, in connection with a unit cell laminated direction S, a first face 142 of the laminated body 140. The first lid member 170 is configured to, if an internal pressure of the cell case 120 is lower than atmospheric pressure, deform while keeping the tightly closing state, come into contact with the first face 142 of the laminated body 140, and apply a pressure based on a differential pressure between atmospheric pressure and the internal pressure of the cell case 120 to the contacting face.