This essay will introduce that how the Korean and Japanese numerals have been developed from the same ancient original words. It would be a big interest for many people who have interested in knowing the orgin of Japanese language of which many Japanese schalors tend to define Japanese language to be one of mysterious ones. This essay however would unveil the orgin of Japanese language refering to the close relation between Korean and Japanese language explained by the writer. Such achievement have been accomplished by the adoption of method of putting the corresponding both countries words in series arrangement developed by the writer.