1. A machine translation apparatus including a plurality of target language document databases used for a translation from an original language to a target language, each target language document database being differently composed from at least one of a plurality of target language documents, comprising: a database control means for setting a non-applied word of translation word's selection to each target language document database, the non-applied word of translation word's selection being a word in the original language that does not require selection using the target language document database from a plurality of translation word candidates of the word, for assigning a priority degree to each of the plurality of target language document databases according to a number of the non-applied word of translation word's selection, and for indicating which of the target language document databases has the highest priority degree; a translation word generation means for generating a plurality of translation word candidates of an original word in an original language document for the translation; a translation word learning means for selecting a translation word as the translation from the plurality of translation word candidates by using the target language document database indicated by the database control means; and an output device for outputting the selected translation word, wherein the database control means sets the non-applied word of translation word's selection to each target language document database according to a user's indication, and the non-applied word of translation word's selection does not require the user's selection from the plurality of translation word candidates when being translated from the original language into the target language.