1. A machine translation apparatus comprising: a document receiving unit that receives an input of a source language document described in a source language; a translating unit that translates the source language document into a translated document described in a target language, and creates an ambiguous portion that is a word or a sentence having an ambiguity occurred during translation; a storing unit that stores the translated document and the ambiguous portion; a speech receiving unit that receives a speech in the source language; a recognition unit that recognizes the speech received by the speech receiving unit and creates a source language speech sentence as a recognition result; a translation updating unit that updates the translated language document stored in the storing unit by retranslating a part of a speech content of the source language speech sentence to which the ambiguous portion corresponds, when the source language document includes the ambiguous portion; and a display control unit that displays the translated document updated by the translation updating unit on a display unit.