1. A machine-translation apparatus comprising: an example storage unit that stores target language examples in a target language and source language examples in a source language in correspondence with one another, each of the target language examples having a meaning equivalent to a meaning of a corresponding one of the source language examples; an input receiving unit that receives an input sentence in the source language; a searching unit that conducts a search in the example storage unit for one of the target language examples corresponding to one of the source language examples that either matches or is similar to the input sentence; a translating unit that generates, using a processor, a reverse-translated sentence by translating the one of the target language examples found in the search into the source language; a detecting unit that detects difference portions between the reverse-translated sentence and the input sentence; a generating unit that generates an output sentence by adding the difference portions to the input sentence; an output unit that outputs, to a user, the output sentence to which the difference portions are added; and a selection receiving unit that receives a selection of one of the output difference portions, wherein; the translating unit further generates a target language sentence by translating a combination of the input sentence and the selected one of the difference portions, and the output unit further outputs the target language sentence.