1. A machine translation system comprising: a translating unit that inputs a sentence and translates the sentence; and a word translation device that performs word translation among a plurality of languages, which word translation device inputs a word included in the sentence that is not translated by the translating unit and translates the word, the word translation device comprising: a storage unit that stores at least a first word search structure, a second word search structure, a first word and translation information record, and a second word and translation information record in a dictionary, the first word search structure being provided for searching for a word of a first language, the second word search structure being provided for searching for a word of a second language, the first word and translation information record including word-associated information and translation information as to words stored in the first word search structure, and the second word and translation information record including word-associated information and translation information as to words stored in the second word search structure; an input unit that inputs a word; a referring unit that refers the input word to the words stored in the first word search structure, wherein the first and second word search structures include first and second links, respectively, for identifying the first and second word and translation information records; an extracting unit that extracts a translation from the translations stored in the second word search structure, based on the first word and translation information record associated with the words, the first word and translation information record retrieved by the extracting unit based on the first link; and an output unit that outputs the extracted translation, wherein the translation information of the first word and translation information record includes a link for identifying a translation stored in the second word search structure or the second word and translation information record, wherein the extracting unit extracts the translation stored in the second word search structure or the second word and translation information record, based on the link included in the first word and translation information record associated with the words referred to by the referring unit, wherein the first and second word and translation information records include records that store one piece of word-associated information and one piece of translation information as to each part of speech for words included in the first and second word search structures, when the words have a plurality of parts of speech, wherein the record of each part of speech is associated with the one piece of word-associated information by a pointer.