PURPOSE: A semi-submersible marine structure is provided to improve the stability and efficiency of a drilling work by preventing the marine structure from moving and rolling on the sea. CONSTITUTION: A semi-submersible marine structure (1) comprises a pontoon (100) and rolling reduction units (300). The pontoon has multiple columns (200) for supporting a deck (D). The rolling reduction units are arranged between the columns formed on the top of the pontoon and reduces the rolling of the marine structure by reducing the exciting force.
