To provide a circuit breaker enabling, with a small force, a release lever to be operated for releasing a wire connected to a quick connection terminal.

In a circuit breaker 1, an auxiliary member 10 is attached to a release lever 9 for releasing a wire connected to a quick connection terminal 5 to make it operable. The auxiliary member 10 includes: a mounting part 10b having an insertion hole 10a for inserting the auxiliary member into the release lever 9; a knob part 10c integrally formed in the mounting part 10b; and a lock part 10d for holding the auxiliary member on a mount panel 11 of a power distribution board 6 while the auxiliary member is not used. Furthermore, a recessed groove 9a is formed on a side surface of the release lever 9 and a projecting line 10e is formed in the insertion hole 10a of the auxiliary member 10 so that, when operating the release lever 9 using the auxiliary member 10, they are prevented from being detached. Moreover, the auxiliary member 10 includes an alignment mark 10f for displaying a position of the insertion hole 10a so as to be easily attached to the release lever 9.