PURPOSE: A horizontal rocking reduction device of a marine structure is provided to improve the efficiency and stability of marine construction and to facilitate the construction work inside a dock and an inner wall. CONSTITUTION: A horizontal rocking reduction device of a marine structure comprises a connection part(110), a damping plate(120), and a reinforcing member(130). The connection part is downward projected from the lower part of the marine structure. The damping plate is connected to the connection part and separated from the bottom part of the marine structure to reduce horizontal rocking. The damping plate is respectively installed along both side of the bottom side. The reinforcing member is fixed to the damping plate and connection part and reinforces the damping plate.
