1. A machine translation apparatus comprising: an input device configured to input a first sentence in a first language; an additional information acquisition unit configured to acquire first additional information relating to a first user, wherein the first additional information comprises a location of the apparatus along with a facility name of the first user, and gender or age information for the first user; a reference data storage device configured to store plural pieces of second reference data each of which associates a second sentence in a second language with second additional information relating to a second user of the second sentence and a usage location of the second sentence; a candidate acquisition unit configured to translate the first sentence in the first language to a plurality of candidates, for a translated sentence, in a second language and acquire confidence scores of the candidates; a text data acquisition unit configured to acquire a plurality of the second sentences from the second reference data stored in the reference data storage device, the plurality of the second sentences being associated with the second additional information each of which is identical with at least a part of the first additional information, the text data acquisition unit configured to determine degrees of similarity between the candidates and the plurality of the second sentences as a function of identifying a correspondence in a number quantity of character n-grams associated with the first sentence and a number quantity of character n-grams associated with each of the plurality of candidates divided by a total number of n-grams that respectively comprise the first sentence and each of the plurality of candidates, and to output a part of the plurality of the second sentences having degrees of similarity equal to or larger than a predetermined value; and an adaptive model learning unit configured to modify an adaptive model representing a trend of machine translation by using the second sentences output from the text data acquisition unit, wherein the second additional information associated with each output second sentence is identical with at least a part of the first additional information; an adaptive translation unit configured to update the confidence scores based on an adaptive score derived from the adaptive model and the confidence scores for each candidate, wherein the adaptive translation unit selects one of the candidates based on updated confidence scores, and an output device configured to output one candidate selected based on the updated confidence scores.