The present invention relates to an apparatus for manufacturing molten irons by injecting fine carbonaceous materials into a melter-gasifier and a method for manufacturing molten irons using the same. The method for manufacturing molten irons according to the present invention includes steps of reducing mixtures containing iron ores in a reduction reactor and converting the mixtures containing iron ores into reduced materials, preparing lumped carbonaceous materials containing volatile matters as a heating source for melting the reduced materials, charging the lumped carbonaceous materials into a dome-shaped upper portion of a melter-gasifier and forming a coal packed bed, preparing fine carbonaceous materials containing volatile matters as a heating source for melting the reduced materials, injecting oxygen and the fine carbonaceous materials into the coal packed bed through a tuyere installed in the melter-gasifier, charging the reduced materials into the melter-gasifier connected to the reduction reactor and manufacturing molten irons, and supplying reducing gas in the melter-gasifier made from volatile matters contained both in the lumped carbonaceous materials and the fine carbonaceous materials to the reduction reactor.