PROTECTIVE CIRCUIT

A protective circuit (A) is provided with: a protective element (A): a plurality or secondary battery cells (), (), . . . ; an external positive electrode terminal () and an external negative electrode terminal (); an auxiliary power supply (); a first controlling dev ice (): and a switch (). The protective element (A) includes: a first fusible conductor () of which the two ends are connected to a first terminal () and a second terminal (): and a heat generating body () disposed in a first energizing path (P) between a third terminal () and a fourth terminal (). The auxiliary power supply () is provided electrically independently of the plurality of secondary battery cells (), (), . . . . In this protective circuit (A), a signal from the first controlling device () causes the switch () to switch in such a way as to conduct electricity, thus causing the heat generating body () of the protective element (A) to generate heat which fuses the first fusible conductor (), thereby isolating the plurality of secondary battery cells (), (), . . . from the external negative electrode terminal ().