PURPOSE: To easily attain a large current and variability in an interrupted current value by providing an electrical bypass element in parallel to a shape memory alloy of high transformation temperature.

CONSTITUTION: A shape memory alloy R1 having a transformation temperature higher than an ordinary temperature is arranged in a circuit provided with a drive contact 1 and a fixed contact 2. In the case of providing a closed circuit by connecting both the contacts, when an overcurrent flows in this circuit, the shape memory alloy R1 is extended or contracted, to displace the drive contact 1 by changing a shape of the alloy separated from the fixed circuit 2, and an open circuit is provided to interrupt the circuit. In this circuit breaker, art electric bypass element R2 is provided in parallel to the shape memory alloy R1. As this bypass element R2, by preparing that of various electric capacities, in an interrupted current value, a large current and variability can be easily and inexpensively attained.