A device for preventing withdrawing and inserting of a circuit breaker, the device comprising: a cradle; a carriage on which circuit breaker electrically connected to the cradle or separated from the cradle; a girder assembly selectively fixed to the cradle; a lead screw coupled between the carriage and the girder assembly and rotated by an external force to allow the carriage to move over the cradle to close a breaker main body or release it; and a breaking unit provided at the girder assembly and preventing the lead screw to operate- characterized in that the braking unit comprises: a plurality of first members provided to be moved in a first direction in which the girder assembly is fixed to the cradle or released therefrom; a second member provided to be separated by a certain distance with respect to the first member and moved in a direction perpendicular to the first direction; and a third member allowing an external force to be transferred to the lead screw while the second member is moving when the first member is fixed to the cradle, and restraining such that the external force cannot act on the lead screw when the first member is released from the cradle, wherein the girder assembly includes a guiding part to allow the second member to move in the second direction, wherein the guiding part comprises: a first plate fixed to the girder assembly; and a guiding pin fixed to the first plate and slidably coupled to the second member in the second direction, and wherein a screw hole is formed at the second member to allow the lead screw to pass therethrough so as to be exposed, and pin holes are formed at both sides of the screw hole to allow the guide pin to be slidably inserted thereinto. a cradle; a carriage on which circuit breaker electrically connected to the cradle or separated from the cradle; a girder assembly selectively fixed to the cradle; a lead screw coupled between the carriage and the girder assembly and rotated by an external force to allow the carriage to move over the cradle to close a breaker main body or release it; and a breaking unit provided at the girder assembly and preventing the lead screw to operate- characterized in that the braking unit comprises: a plurality of first members provided to be moved in a first direction in which the girder assembly is fixed to the cradle or released therefrom; a second member provided to be separated by a certain distance with respect to the first member and moved in a direction perpendicular to the first direction; and a third member allowing an external force to be transferred to the lead screw while the second member is moving when the first member is fixed to the cradle, and restraining such that the external force cannot act on the lead screw when the first member is released from the cradle, wherein the girder assembly includes a guiding part to allow the second member to move in the second direction, wherein the guiding part comprises: a first plate fixed to the girder assembly; and a guiding pin fixed to the first plate and slidably coupled to the second member in the second direction, and wherein a screw hole is formed at the second member to allow the lead screw to pass therethrough so as to be exposed, and pin holes are formed at both sides of the screw hole to allow the guide pin to be slidably inserted thereinto. a plurality of first members provided to be moved in a first direction in which the girder assembly is fixed to the cradle or released therefrom; a second member provided to be separated by a certain distance with respect to the first member and moved in a direction perpendicular to the first direction; and a third member allowing an external force to be transferred to the lead screw while the second member is moving when the first member is fixed to the cradle, and restraining such that the external force cannot act on the lead screw when the first member is released from the cradle, wherein the girder assembly includes a guiding part to allow the second member to move in the second direction, wherein the guiding part comprises: a first plate fixed to the girder assembly; and a guiding pin fixed to the first plate and slidably coupled to the second member in the second direction, and wherein a screw hole is formed at the second member to allow the lead screw to pass therethrough so as to be exposed, and pin holes are formed at both sides of the screw hole to allow the guide pin to be slidably inserted thereinto. a first plate fixed to the girder assembly; and a guiding pin fixed to the first plate and slidably coupled to the second member in the second direction, and wherein a screw hole is formed at the second member to allow the lead screw to pass therethrough so as to be exposed, and pin holes are formed at both sides of the screw hole to allow the guide pin to be slidably inserted thereinto.