A coupling device for a circuit breaker, comprising: an outer handle assembly installed outside a distribution board having a circuit breaker body; an inner handle rotatably installed at the circuit breaker body, and configured to manipulate a circuit breaker; and a coupling assembly installed between the outer handle assembly and the inner handle, and configured to transmit a rotational force of the outer handle assembly to the inner handle, wherein the coupling assembly includes: a first coupler coupled to the outer handle assembly; and a second coupler coupled to the inner handle, and restricted by the first coupler in a shaft direction; characterized by: a third coupler coupled between the first coupler and the second coupler, and configured to transmit a rotational force applied to the first coupler to the second coupler, wherein one or more first coupling protrusions, which protrude from the outer handle assembly in the shaft direction, are formed at the first coupler, wherein one or more second coupling protrusions, which protrude from the outer handle assembly in the shaft direction in correspondence to said one or more first coupling protrusions, are formed at the second coupler, and wherein the third coupler is inserted between said one or more first coupling protrusions and said one or more second coupling protrusions, and wherein an overlapped length between said one or more first coupling protrusions and said one or more second coupling protrusions in the shaft direction is longer than a contact length between said one or more first coupling protrusions and the third coupler in the shaft direction or between said one or more second coupling protrusions and the third coupler in the shaft direction. an outer handle assembly installed outside a distribution board having a circuit breaker body; an inner handle rotatably installed at the circuit breaker body, and configured to manipulate a circuit breaker; and a coupling assembly installed between the outer handle assembly and the inner handle, and configured to transmit a rotational force of the outer handle assembly to the inner handle, a first coupler coupled to the outer handle assembly; and a second coupler coupled to the inner handle, and restricted by the first coupler in a shaft direction; characterized by: a third coupler coupled between the first coupler and the second coupler, and configured to transmit a rotational force applied to the first coupler to the second coupler, wherein one or more first coupling protrusions, which protrude from the outer handle assembly in the shaft direction, are formed at the first coupler, wherein one or more second coupling protrusions, which protrude from the outer handle assembly in the shaft direction in correspondence to said one or more first coupling protrusions, are formed at the second coupler, and wherein the third coupler is inserted between said one or more first coupling protrusions and said one or more second coupling protrusions, and a third coupler coupled between the first coupler and the second coupler, and configured to transmit a rotational force applied to the first coupler to the second coupler, wherein one or more first coupling protrusions, which protrude from the outer handle assembly in the shaft direction, are formed at the first coupler, wherein one or more second coupling protrusions, which protrude from the outer handle assembly in the shaft direction in correspondence to said one or more first coupling protrusions, are formed at the second coupler, and wherein the third coupler is inserted between said one or more first coupling protrusions and said one or more second coupling protrusions, and