This study analyzed which factors mainly affect population change by using the Bayesian APC model, which classifies each mesh population change into three factors-age, period, and cohort-based on changes in national population composition from 2000 to 2015. According to the analysis of the mesh of more than 100 people in Kashiwa City and Tsukuba City, the main factors of population change were the "age effect" and "period effect" along with the "cohort effect". By assessing the range of the age effect, it is possible to determine which age section from the population composition ratio of the mesh is larger with respect to the national trend. As a result, the development of facilities to support residential and living environments should be considered.