1. A method of 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 method comprising: an input step in which one or more keywords in the source language are input via an input means 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 sentence pair extraction step in which a sentence pair extraction means extracts one or more sentence pairs each including more than one of the keywords from 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 keyword-related phrase storage step in which a target-language keyword-related phrase corresponding to each source-language keyword-related phrase is detected from the partial correspondence information of each sentence pair and stored as a pair of keyword-related phrases in the source language and in the target language in the form of a keyword-related phrase table in a storage means; a text sentence candidate generation step in which a text candidate generation means performs dependency relationships of each keyword-related phrase in the source language and in the target language of the pair of keyword-related phrases 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 by using a target language keyword-related phrase generation model and a language model by assuming dependency relationships of two or more pairs of keyword-related phrases; and an output step in which at least one text sentence candidate is output from an output means corresponding to the full text sentence in the source language.