Household is a unit of economy and society. Various studies have been conducted on its changes. However, its data are scarce and its measurement methods have not integrated. The reason for this situation may be the necessity to simultaneously consider both the number of households and the size distribution of households to investigate its changes. Researches from these two viewpoints have not been conducted. Objectives of this research are (1) the estimation of the average size of migrating households, and (2) the determinant analysis of its time-series variation. A Markovchain model of inter-prefectural household migration is constructed and on this basis, the average sizes of (1) staying households, (2) migrating households within prefectures and (3) inter-prefecturally migrating households, are estimated. The determinant analysis of their variations shows that they are influenced by life-events such as marriage and university-enrolment and by general economic conditions like GDP growth rate. A change in the causal structure is also found during periods of the oil-crisis and the collapse of the bubble economy.