Provided is a trip button mechanism of an external handle for a circuit breaker. The trip button mechanism includes a button support, an externally operable trip button, and an elastic member. The button support is disposed at an outer casing of the externally operable handle and exposed through a penetration hole of the outer casing. The externally operable trip button includes a handle exposed through the penetration hole and a pusher in one piece with the handle. The pusher is movable along the button support for pushing a circuit breaker trip button. The elastic member applies a force to the externally operable trip button in a direction opposite to a direction in which the externally operable trip button pushes the circuit breaker trip button. Therefore, the trip button mechanism can be easily assembled to increase productivity and decrease manufacturing costs, and the trip button mechanism can be reliably operated.