PURPOSE: To reduce the memory capacity of a dictionary and to improve the ratio of conversion by composing this device of a first storage device as a self-contained language dictionary, second storage device as an adjunct dictionary, and third storage device for temporary storage used for conversion processing.

CONSTITUTION: This device is provided with a storage device 41 to store the information of 'reading', 'Chinese character (KANJI) description' and 'part of speech for self-contained language' of the self-contained language and a storage device 42 to store the information of the 'reading', 'KANJI description', 'part of speech for the self-contained language to be connected' and 'part of speech for adjuncts' of the adjuncts. Then, this device is equipped with a means to retrieve the adjunct or the combination of adjuncts, means to retrieve the self-contained language, means to convert the 'KANJI description' of the retrieved independent word and the 'KANJI description' of the adjunct to the character string of a KANJI and Japanese syllabary (KANA) mixing sentence, and storage device 43 for information to be temporarily stored in the case of retrieval/conversion processing. Thus, the Japanese conversion device reducing the memory capacity of the dictionary and improving the ratio of conversion can be provided.