PURPOSE: To reduce the processing of sentence analysis by deleting a word candidate which agrees with a part of a specified word and reducing the number of the combination of words which are identified.

CONSTITUTION: A word extraction means 10 collates the word from a dictionary storing information on the notation, reading and grammar of multiple words with the character string of an input sentence being KANJI (Chinese character)/ KANA (Japanese syllabary)-mixed sentence, and it extracts all the words which agree with a part of the character string. A word candidate reduction part 20 deletes only the words which agree with a part of the previously designated word among the extracted words from the word candidates, and it inputs the extracted words excepting the previously designated word to a sentence analysis part 30 as the word candidates. The sentence analysis part 30 selects and reads the word which is most grammatically certain from the word candidates and outputs the character string. Thus, processing quantity can be reduced.