To prevent an excessive internal pressure rise of a secondary battery main body.

The secondary battery main body 20 is stored in internal space between a battery case 10 and a cover 11. A temperature sensor 27 is fixed to an outer surface of the secondary battery main body 20, when the temperature sensor 27 detects a high temperature ≥60°C and a voltage of the secondary battery main body 20 is detected to be ≥4.1 V, an FET of a discharge circuit is turned on to suppress battery voltage below a decomposition voltage of electrolyte.