1. A domain-adaptive portable machine translation device for closed captions, comprising: a keyword extraction part extracting keywords for recognizing style and domain of a caption sentence in an input broadcast signal; a style and domain recognition part recognizing the style and domain of the caption sentence based on the extracted keywords, a pre-constructed predicate ending/style statistical dictionary and a pre-constructed vocabulary/domain statistical dictionary; a dynamic translation knowledge construction part dynamically constructing translation knowledge based on the recognized style and domain, and then loading the result into a dynamic translation DB of a main memory; a dynamic translation module construction part dynamically constructing a translation module based on the recognized style and domain; a morpheme analysis part analyzing morphemes of the caption sentence under the control of the dynamic translation module construction part; a sentence pattern application part performing sentence-by-sentence translation by applying a sentence pattern to the caption sentence under the control of the dynamic translation module construction part; a syntax analysis part analyzing syntax of the caption sentence under the control of the dynamic translation module construction part; and a pattern-based translation generation part producing a pattern-based translation of the caption sentence based on the syntax analysis result.