This paper develops a population forecasting model for the Chugoku region in Japan, highlighting the consistent structure of interregional migration, and the effects of economic disparity between regions. By considering the changes in out-migration rate by age, the results show that population aging causes a reduction in interregional migration, which leads to natural demographic change dominating. Moreover, it is predicted that elderly people will rapidly increase by 24% in Hiroshima prefecture due to the aging of post-war baby boomers that had inflow during the rapid growth period, and so again natural demographic change will become increasingly significant. The forecasts of other institutions, which assume that the net migration rate during 2005-2010 will remain constant in the future, are more pessimistic than the results found in this paper. Lastly, the change in the fertility rate may affect the prefectural population in the Chugoku region in 2050 by around 10%.