The aim of this paper is to investigate the factors of inter-prefectural migration in Japan from point of the population size of prefectures. The main results are as follows.
① To introduce the point of population size is very useful to investigate the inter-prefectural migration.
② "Standard rate of migration", which reflects the sex- and age-structure of a prefecture and is formulated originally at this paper, is a very useful tool to analyze the migration.
③ "Rate of moving into" has the very close correlation with the size of population, the income disparity, and the "standard rate of migration".
④ "Rate of moving out" has only a little correlation with the population size and the income disparity, and has little correlation with the "standard rate of migration" and the growth rate of establishment.
⑤ Because of mutual, dose correlation among the size of population, the income disparity and the "standard rate of migration", we must pay much attention to partial regression coefficients in multiple regression analysis of "moving into or out" with these factors as explanatory variables.