A thin battery is configured with improved durability of foil-like electrode terminals. The thin battery has an electricity-generating element housed inside a battery outer casing with a pair of electrodes of the electricity-generating element being connected to electrode terminals that extend out from the outer edges of the battery outer casing. The electrode terminals have a base portion located partially with the battery outer casing and a tip portion spaced from the battery outer casing with strength transition point being formed between the base portions and the tip portions. The strength transition points of the electrode terminals are positioned to the outside at some distance away from the outer edge of the battery outer casing.