To enable to decrease the number of component parts, downsize a whole body, and facilitate assembling work.

The circuit breaker is provided with a breaker body 2 with a cross-section of nearly a concave shape, one of the terminals 3 integrally built in at a lower part of the breaker body 2, a thermistor 5 arranged on the terminal 3, a curved bimetal 6 loaded on the thermistor 5, and a composite member 7 with a spring 13 integrally prepared at one side edge of a cover 12 closing a top opening of the breaker body 2 and bent downward and with the other terminal 11 integrally formed at the other side edge of the cover 12. At the tip of the spring 13 in the composite member 7, a contact member 13a in contact with the terminal 3 is fixed.