Disclosed is multipurpose ozone treatment method and apparatus for a ship, which are capable of performing many treatments such as the purification of using-water used in the ship and wastewater generated during the ship voyage, the purification of harmful gas generated during engine operation of the ship or generated from internal space of the ship, and the refinement of remaining fuels supplied to the engine of the ship, by utilizing the sterilizing power of ozone gas generated from one ozone generator, which is employed for processing and sterilizing ship ballast water. Since the ozone gas generated from the ozone generator can be controlled at a proper concentration and then it can be supplied for treating ship ballast water, using-water, wastewater, noxious gas and remaining fuel due to operation of the mass flow controller, then economic efficiency and economic feasibility of the multipurpose treatment using ozone gas generated from one ozone generator can be highly improved, thereby improving convenience in use for various concentrations of ozonated water as well as significantly reducing the cost and time spent for the treatment.