The present invention provides an apparatus for solidifying and converting carbon dioxide into carbonate, comprising: an alkali component extraction reactor for extracting an alkali metal component from a raw slag; a carbonation reactor for injecting carbon dioxide into an alkali metal component solution containing the extracted alkali metal component to produce a carbonate precipitate from the alkali metal component solution; a first filtration device connected between the alkali component extraction reactor and the carbonation reactor to separate a post-treatment slag, from which the alkali component is extracted, from the alkali metal component solution; and a second filtration device connected between an inlet of the alkali component extraction reactor and an outlet of the carbonation reactor to separate the carbonate from the alkali metal component solution after the carbonation reaction.