13. An apparatus for generating a text sentence in a target language different in a source language, based on one or more words in the source language input as keywords, the apparatus comprising: input apparatus for inputting one or more keywords in the source language without inputting a full text sentence in the source language, the one or more keywords being a segment of the full text sentence in the source language; a parallel corpus database including partial correspondence information indicating correspondence between a word/phrase in the source language and a word/phrase in the target language in each sentence pair; a sentence pair extraction means for extracting one or more sentence pairs each including more than one of the keywords from the parallel corpus database; a keyword-related phrase storage means for detecting a target-language keyword-related phrase corresponding to each source-language keyword-related phrase from the partial correspondence information of each sentence pair and storing the detected target-language keyword-related phrase in the form of a keyword-related phrase table; a text candidate generation means that performs dependency relationships of each keyword-related phrases in the source language and in the target language of the pair of keyword-related phrases described in the keyword-related phrase table and generates one or more target-language sentence candidates by using a target language keyword-related phrase generation model and a language model by assuming dependency relationships or two or more pairs of keyword-related phrases; and an output means for outputting at least one text sentence candidate corresponding to the full text sentence in the source language.
13. An apparatus for generating a text sentence in a target language different in a source language, based on one or more words in the source language input as keywords, the apparatus comprising: input apparatus for inputting one or more keywords in the source language without inputting a full text sentence in the source language, the one or more keywords being a segment of the full text sentence in the source language; a parallel corpus database including partial correspondence information indicating correspondence between a word/phrase in the source language and a word/phrase in the target language in each sentence pair; a sentence pair extraction means for extracting one or more sentence pairs each including more than one of the keywords from the parallel corpus database; a keyword-related phrase storage means for detecting a target-language keyword-related phrase corresponding to each source-language keyword-related phrase from the partial correspondence information of each sentence pair and storing the detected target-language keyword-related phrase in the form of a keyword-related phrase table; a text candidate generation means that performs dependency relationships of each keyword-related phrases in the source language and in the target language of the pair of keyword-related phrases described in the keyword-related phrase table and generates one or more target-language sentence candidates by using a target language keyword-related phrase generation model and a language model by assuming dependency relationships or two or more pairs of keyword-related phrases; and an output means for outputting at least one text sentence candidate corresponding to the full text sentence in the source language. 20. The apparatus according to claim 13 , wherein each time one keyword is input via the input means, the sentence pair extraction means and the keyword-related phrase storage means operate, the apparatus further comprising: a co-occurrence word extraction means for extracting one or more co-occurrence words which co-occur with the keyword in the sentence pair and describing the extracted one or more co-occurrence words in a co-occurrence word table; and a co-occurrence word presentation means for presenting the one or more co-occurrence words to a user such that the user can select one or more co-occurrence word from the co-occurrence words described in the co-occurrence word table, and wherein if one or more co-occurrence words are selected by the user via the input means, the selected one or more co-occurrence words are input as new keywords, and the text candidate generation means operates after completion of inputting all keywords, wherein the text candidate generation means assumes dependency relationships among keyword-related phrases in the target language described in the keyword-related phrase table and generates one or more target-language text sentence candidates, the apparatus further comprising source-language text candidate generation means that assumes dependency relationships among keyword-related phrases in the source language described in the keyword-related phrase table and generates one or more source-language text candidate, and wherein at least one set of text sentences in the source and target languages is output from the output means.