Abstract: [OBJECT] An object is to inspect leak of a film-sheathed battery 21 surely in a short time in a stage in which a battery module 1 has been assembled. [SOLUTION TO PROBLEM] A battery module 1, which is formed by arranging a plurality of flat film-sheathed batteries 21 in layers and accommodating them in a case 11, has a slit at one end of a longitudinal direction, and a gas sensor 3 is inserted into this slit. A terminal portion 12 that is positioned at the other end of the longitudinal direction has a bolt hole that communicates with an inside of the case 11, and a blower 2 is connected to this bolt hole. Air is compulsorily introduced into the case 11 by the blower 2. The air passes through a periphery of the gas sensor 3, and flows out of the case 11. Therefore, the presence or absence of the leak can immediately be judged from an output of the gas sensor 3.