The Nationality Law was approved in 1899, and the permission of naturalization was published by Government Newsletter (Kanpo) since 1900 in Japan. Using 407,397 sample data since 1940 to 2009, we try to clarify the changes and regional difference of naturalized population in Japan.
The total naturalized population in periods of both 1970-79 and 1980-89 are all less than 70,000 persons, but it increase to 118,848 in 1990-99 and exceeds 150,000 in 2000-09. On the regional difference, naturalized population in the prefectures such as Osaka, Tokyo, Hyogo, Kanagawa, Aichi, Kyoto, Fukuoka, Saitama and Chiba, most of which are located in the three main metropolitan areas, exceed 10,000 persons as a total of 1970 to 2009. The continuous increase in Osaka, Hyogo and Kyoto in the four periods can be considered as a result of concentration of Korean old-comers in these prefectures. During the fourth period of 2000-09, change in the naturalized population distribution appeared and the population in the prefectures of Nagano, Shizuoka, Gifu, Shiga, Hiroshima and Yamaguchi exceed 2,000 persons, but, Hokkaido and all the prefectures in Tohoku Region and Shikoku Region remain on the low level of less than 1,600 persons.