NOVELTY - The structure has a lower support part (20) comprising a lower hollow space formed in a lower concrete part provided on a base (4) installed on a sea floor (3), and a lower inner-pipe attached to a circumferential inner surface of the lower hollow space. A main body part (10) is coupled to an upper end of the lower support part. The main body part comprises a main-body inner-pipe attached to a circumferential inner surface of a main-body hollow space, where the lower inner-pipe and the main-body inner-pipe are made of steel or fiber reinforced plastic.    USE - Supporting structure for an offshore wind power generator installed on a sea floor.    ADVANTAGE - The furnace slag is used as bonding agent having high degree of fineness, so that mobility of the main-body concrete part and the lower concrete part can be ensured while preventing separation of substances constituting the concrete parts by providing large surface area, thus appropriately maintaining viscosity of the structure. The concrete parts are supported by the inner-pipes in a tri-axial compression load state of the structure, thus enhancing rigidity of the structure with respect to bending moment and improving resistance to a transverse load. The weight of the structure can be reduced by formation of the hollow space, thus reducing material cost. The structure can be modularized, so that the assembly and construction cost can be minimized.    DETAILED DESCRIPTION - The lower concrete part and the main-body concrete part are formed by mixing cement ranging from 400-450 kilogram per cubic meter, furnace slag ranging from 100-350 kilogram per cubic meter, mixing water ranging from 180-230 kilogram per cubic meter, fine aggregate ranging from 600-700 kilogram per cubic meter, coarse aggregate ranging from 800-900 kilogram per cubic meter and admixture ranging from 4-8 kilogram per cubic meter, where the admixture comprises a mixture of cellulose-based viscosity agent, acryl-based viscosity agent, polyethyleneoxide-based viscosity agent and propylene carbonate.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic view of a supporting structure for an offshore wind power generator installed on the sea floor.    Tower (1)    Impeller (2)    Sea floor (3)    Base (4)    Main body part (10)    Lower support part (20)    Upper support part (30)