With a battery using a flexible outer package, electric current is reliably interrupted when the temperature is increased due to the occurrence of abnormality, thereby preventing excessive heat generation. A battery 1 includes a battery element 10, a pair of first terminals 11 that are electrically connected to the battery element 10, a flexible outer package 13, and a second terminal 12. The outer package 13 is partitioned into a first chamber 13a in which the battery element 10 is sealed and a second chamber 13b which is adjacent to the first chamber 13a. The second terminal 12 is led out from the second chamber 13b to the outside of the outer package 13 so that one first terminal 11 is made electrically connectable to an external wiring through the second chamber 13b. A gas generation material 14 which generates a gas at a predetermined temperature or higher is sealed in the second chamber 13b.