1. An apparatus for automatic translation, comprising: a knowledge extracting part for extracting knowledge necessary for translating sentences constituting a document in a restrictive domain; and a translating part for generating an output for an input sentence based on a dictionary and a transformation pattern to which the extracted translation knowledge is applied, wherein the knowledge extracting part comprises: a technical term constructing part for extracting and constructing technical terms by constructing a corresponding corpus according to the document in the restrictive domain through morpheme-analyzing and tagging; a translated term constructing and filtering part for applying a weight and extracting a high-frequency expression by a longest-first method, filtering a sentence/phrase pattern, and constructing translated words for the constructed technical terms; and a sentence/phrase pattern constructing part for constructing a syntax translation pattern and a sentence translation pattern of a corresponding domain according to a frequently repeated word string and example based on the corresponding corpus.