CIRCUIT BREAKER

PURPOSE:To perform a stable trip action by securing a containing space for an energization spring sufficiently even when an overcurrent tripping means of a circuit breaker is compact. CONSTITUTION:Recessed parts 21c and 22e are formed in attraction couter surfaces of an anvil 21 and a plunger 22 of an electromagnetic trip part 102, and an energization spring 23 is assembled between these recessed parts 21c, 22e. When a large current flows, a magnetic force excited by a coil 16 of the electromagnetic trip part 102 gets over an energization force of the spring 23 to attract the plunger 22 to the anvil 21, so an opening mechanism part 4 is forcedly rotated to trip a circuit breaker. A containing height H2 for the energization spring can be set to be large, and a sufficient energization force can be secured, with a spring constant set small, thereby the circuit breaker can be compact and of high performance.