Regional population change reflects adaptation process of the people to their environment. In this study, to clarify the regional characterization of the administrative units in Yamanashi prefecture, which abounds in mountainous areas, their population changes from 1920 to 1995 were analyzed to relate with the landform and the industrial structure. Population change of Yamanashi prefecture as a whole is divided into three phases, rapid increase in 1940-47, decrease in 1947-65 and increase in 1970-95. Based on the patterns of population change in these three phases, the administrative units were categorized into six groups (A, B, C, D1, D2, and E). The administrative units of the group A, in which the secondary and tertiary industries were already dominant in 1920, constantly increased population, though the increase in 1940-47 was small. After a rapid increase of population in 1940-47, the group E also showed gradual increase of population with change in industrial structure from the early time. In contrast, the groups B (with stable population in 1940-47) and C (with rapid increase of population in 1940-47), which were characterized by narrow flatlands area, have decreased population since 1947 due to less development in any industries. The groups D1 (with a high proportion of flatlands) and D2 (with an intermediate proportion of flatlands) have also decreased population since 1947, though the former has shown a rapid population increase since 1965 in accordance with rapid change in industrial structure and the latter has gradually increased population since 1970, remaining relatively high dependence on the primary industry. In summary, the variation in change of regional population has been basically related to the local industrial structure. In addition, however, the proportion of flatlands has profoundly affected the regional difference in population change through change of industrial structure.
