2. The apparatus according to claim 1 , wherein the syntactic structure is a parse forest including a plurality of parse trees that are adoptable based on predetermined grammatical rules used for the syntactic analysis of the source language sentence.
2. The apparatus according to claim 1 , wherein the syntactic structure is a parse forest including a plurality of parse trees that are adoptable based on predetermined grammatical rules used for the syntactic analysis of the source language sentence. 3. The apparatus according to claim 2 , wherein: the syntax analyzing unit generates the parse forest that includes the parse trees, wherein the parse trees have respective second plausibilities associated therewith representing certainties of the respective parse trees; the first extracting unit extracts the first sub-string from a parse tree, of the parse trees, for which a second plausibility is greater than a predetermined first threshold value; and the second extracting unit extracts the second sub-string from the parse tree for which the second plausibility is greater than the predetermined first threshold value.