The purpose of this article is to examine Kanazawa Syousaburou's study on 「the Korean language」. In the early years of Meiji period, the Japanese government exploited Donjoron (a theory of the common ancestry of the Japanese nation and the Korean nation) as a political ideology to orient to a multi-national country and achieve national unity, in the process of making 「the Japanese language」 established as 「the national language」. Japan's success in modernization led to the invasion and colonization of its neighboring countries, and the Meiji government made its utmost effort to arrange the system as a nation-state and, at the same time, to achieve national unity as a multi-national country. In modern Japan, 「the national language」 meant 「the Japanese language」, and 「the national language」 was considered with national identity and historicity incorporated into its meaning, like 「national spirit」. In this process, Japan realized that there was a need to criticize its traditional Japanese in terms of national language education and the system of national language studies and to re-establish the language as the standard language of a multi-national country. Particularly, Kanazawa Syousaburou made a great contribution to the national unity policy of the Japanese government through the linguistic research of its Asian neighbors centering upon the Japanese language. His linguistic research, with the languages of Ainu, Ryuukyuu and Korea as subjects, was noticeably political, in that those languages became the languages of colonial countries and Japanese land through the invasion. Kanazawa made an intensive study on the Ainu language at the college of liberal arts of Tokyo Imperial University. Kanazawa, who had already won recognition as a scholar while in college, was dispatched to Hokkaido for research by the government. In 1902, he wrote an article entitled ??A Comparative Study on Korean and Japanese??, and he became very famous because he proved that the two languages had originated from the same root. Subsequently, he had been dispatched for the three years from 1898 for the research on the Korean language, and in 1903 he, as a member of National Language Research Committee of the Education Ministry, was sent to Ryuukyuu for the research on its language. Published in 1912, ??A Study on Japanese Grammar?? was the fruit of his comparative study on the languages of Ainu, Korea, and Ryuukyuu. In 1929 when Japan was forced to modify its colonial policy as it failed in the policy and faced a strong criticism from home and abroad, Kanazawa presented「Il-Seon Dongjoron」(A theory of the common ancestry of the Japanese nation and the Korean nation). This academic fruit, which served as a political ideology justifying Japan's invasion of Asia, had great repercussions in the then society, leading to his gaining a great reputation as a scholar. In the year, Kanazawa's individual comparative study on languages culminated. Before that, however, the Japanese government had already decided to stop the student registration of the department of the Korean language, filled up to its capacity over the years, and in 1927 closed the department. Consequently, the Japanese government turned its back on his academic achievements, which could not politically exploited any more for its colony assimilation policy. As a result, he insisted that the department be maintained, while arguing that it was difficult to Japanize other nations within Japanese land through Japanese education and to assimilate them. He chose to correspond his study to the Japanese government's political intention himself, but as his theory was of no utility value, it was reduced to an object of criticism. It is understood that the essence of Kanazawa's comparative study on the languages of Ainu, Korea and Ryuukyuu lay in his own effort to solve the problem of how to incorporate the minority in Japanese land. Therefore, it gives a warning that the respect and protection of each nation's proper culture is a priority task for the multi-national country-oriented Japanese government to pursue.