PURPOSE: To obtain a Japanese input device which provides conversion of a kana (Japanese syllabary) word into a corresponding kanji (Chinese character) word by using a basic dictionary memory and exclusive-use dictionary memory by providing both memories.

CONSTITUTION: When an operator input a word of some Japanese letters from keyboard 4, it is displayed on display unit 1 and after the input operation ends, a kana-kanji conversion key is depressed. Then, a conversion program is started to retrieve 6-A assigned among exclusive-use dictionary memories and when a corresponding word is found, a "kanji" word in the 1st order is displayed 1. If this is not the corresponding word, all kanji words in basic dictionary memory 5 corresponding to the word of said Japanese letters are read out and displayed. The operator uses selectively a required kanji word among them and also stores them in several exclusive-use dictionary memories while giving an order from the latest-used one by technical fields. Consequently, input operation after appropriate kana-kanji conversion is simplified.