BATTERY PACK

Provided is a battery pack containing a cylindrical battery, achieving sufficient strength while avoiding increase in size. The battery pack includes cylindrical battery (), a circuit board, and an exterior case including first case () and second case (). First case () has a curved portion along an outer peripheral surface of cylindrical battery () and first vertical wall () connected to an end edge of the curved portion. Second case () has second vertical wall () connected to first vertical wall (). First vertical wall () has fitting protrusion () protruding from opposed surface () facing second vertical wall (). Second vertical wall () has fitting groove () that is formed in opposed surface () facing first vertical wall () and that guides fitting protrusion (). Fitting protrusion () is guided into fitting groove (), and first vertical wall () and second vertical wall () are welded together. First vertical wall () has inner surface () in a concave shape along a surface of cylindrical battery (), and a leading end portion with opposed surface (), being thicker than curved portion ().