To provide a breaker switch sensitive to an abnormal temperature rise.

As for a breaker switch disposed on the wall of an electrical apparatus, the breaker switch contains a receptacle containing thermoplastic composition having a softening point θ1, and a flexible metal strip 10 intervening between two studs to be connected to the wall with its one end. This flexible metal strip 10 is extended over the receptacle, its free part is provided with a means to lock itself in the thermoplastic composition, and is bent so as to be brought into contact with the two studs. It is advantageous that the receptacle is extendedly formed by a thermal probe heading toward a core part of the apparatus. If the temperature of the apparatus exceeds the softening point θ1, the locking means is released from the thermoplastic composition by restoring force of the strip, and thereby contact between the studs is released. This breaker switch is applicable to a battery, a lithium ion type battery in particular.