This is Ssangsin Blockade Machine used between one station and another on the double-track lines for safe operation of a train. It was established at Yeongdeungpo Station in October, 1905, but having found that it had a low degree of stability, the machine stopped its operation and was replaced by the special Ssangsin blockade machine in 1932. The machine has been displayed from the year of 1936 at the Railroad Museum, attached to the Training School for Railroad Workers, was established and has a historic value as a relic.