1. A communication supporting apparatus comprising: an input accepting unit that accepts a source language sentence to be translated input by a user; a paraphrase knowledge storing unit that stores paraphrase knowledge in which a source language interpretation which is an interpretation of the semantic content of the source language sentence is associated with a paraphrase interpretation having the same semantic content as the source language interpretation and a different expression form; a source language analyzing unit that analyzes the semantic content of the input source language sentence and outputs the source language interpretation; a paraphrasing unit that obtains the paraphrase interpretation associated with the output source language interpretation from the paraphrase knowledge storing unit, and paraphrases the input source language sentence in a source language paraphrase sentence based on the obtained paraphrase interpretation; and a translation unit that translates the output source language interpretation into a first target language sentence and translates the obtained paraphrase interpretation into a second target language sentence.