To improve a battery safety by discharging a battery in the case of an abnormal increase in a battery temperature, and controlling such a trouble that electrolyte solution is ejected.

This automatic discharge device 1A assembled in a battery case is provided with an operation conductive element 4 for leading a circuit at a prescribed temperature, and a discharge element 3 connected in parallel to the battery the operation conductive element 4. In the operation conductive element 4, a coil spring 45 is disposed as an elastic means for making in an initial condition a condition in which elastically energizing motion is suppressed by interposing a temperature sensor 46, and the circuit is led by moving a contact 43 actuated by the elastically energizing motion of the coil spring 45 released by fusion of the temperature sensor 46 at the time of over-heat. While, a operation-switching element is provided so as to switch over the conductive circuit to an operation conductive circuit from an initial conductive circuit at a prescribed temperature, and the initial conductive circuit is connected in series to the battery, and the operation-conductive circuit is connected in parallel to the battery through the discharge element 3.