24 is sprung up in fig9 a reference symbol 22 u2032 represents the heating agent casing after it has been moved upward for this reason the electrical connection between the heating agent casing 22 and the first bus bar 11 and the second bus bar 14 is rendered ineffective namely it results that the first bus bar 11 and the second bus bar 14 are electrically out off whereby the electric circuit of the vehicle is broken in this way according to the circuit breaker of the embodiment since each of the multi contact springs 21 a 21 b has a small resistance to contact even when a large current passes therethrough it is possible to lessen the generation of heat also since the insert draw off forces thereof are small even when the heating agent casing 22 is moved vertically the heating agent casing 22 can easily rise due to a small sliding resistance of the multi contact springs namely because of the sliding resistance of each multi contact spring 21 a 21 b the electric circuit of the vehicle can be broken reliably in a short time to make it possible to protect the relevant electric parts further because of the use of the thermit reaction heat of the heating agent 23 it is possible to provide the circuit breaker with a simple structure also because the external stress that has been applied to the first bus bar 11.