An externally operable handle assembly including a trip button mechanism for operating a circuit breaker trip button of a circuit breaker, the trip button mechanism comprising: a button support disposed at an outer casing of the externally operable handle assembly; an externally operable trip button movable along the button support for manipulating the circuit breaker trip button; and an elastic member applying an elastic 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, wherein the externally operable trip button comprises: a handle exposed through a penetration hole formed in the outer casing; and a pusher formed in one piece with the handle and movable along the button support for selectively pushing the circuit breaker trip button; wherein the button support comprises: a first space in which the handle is placed, the first space communicating with an outside of the outer casing through the penetration hole of the outer casing; characterized in that the button support further comprises: a second space communicating with the first space in a vertical direction, the second space communicating with an inside of the outer casing through an opening formed in two mutually facing sides of the button support, a portion of the pusher being disposed in the second space. a button support disposed at an outer casing of the externally operable handle assembly; an externally operable trip button movable along the button support for manipulating the circuit breaker trip button; and an elastic member applying an elastic 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, wherein the externally operable trip button comprises: a handle exposed through a penetration hole formed in the outer casing; and a pusher formed in one piece with the handle and movable along the button support for selectively pushing the circuit breaker trip button; a handle exposed through a penetration hole formed in the outer casing; and a pusher formed in one piece with the handle and movable along the button support for selectively pushing the circuit breaker trip button; wherein the button support comprises: a first space in which the handle is placed, the first space communicating with an outside of the outer casing through the penetration hole of the outer casing; a first space in which the handle is placed, the first space communicating with an outside of the outer casing through the penetration hole of the outer casing; characterized in that the button support further comprises: a second space communicating with the first space in a vertical direction, the second space communicating with an inside of the outer casing through an opening formed in two mutually facing sides of the button support, a portion of the pusher being disposed in the second space. a second space communicating with the first space in a vertical direction, the second space communicating with an inside of the outer casing through an opening formed in two mutually facing sides of the button support, a portion of the pusher being disposed in the second space.