The Japanese fertility rate has been below the replacement level for about 30 years. If fertility rate immediately returned to the replacement level, ultimate level of total population would be lower than present. The ratio of the ultimate level to present is called as "population momentum". In many cases, the population momentum is calculated with whole Japanese population. But if we recognize Japanese population as a group of some regional populations, we must consider the differences of fertility or mortality levels among the group and the effects of internal migrations. Analyzing the effects of considering these factors is important because these kinds of analyze have not been broadly performed to Japanese population and will also give broader aspects of Japanese population. In this paper, multiregional population model for Japan is constructed. And theoretical background of the spatial momentum is presented. Using this model and theory, Japanese spatial momentum is evaluated with recent available data. The main findings in this paper are as follows. 1. Spatial momentum in Japan is slightly lower than usual population momentum. 2. Stationary level or trajectory to stationary of each region of population is different between in multiregional population model and in regionally closed population model. 3. Decreasing the level of internal migration lowered the spatial momentum because high fertility region get more dominating in whole population with that change. 4. Expanding the difference with decreasing fertility rate on local areas lowered the spatial momentum because the populations in those areas get to converge lower level. In this paper, many characteristics of Japanese spatial momentum with recent available data, which ordinary population momentum does not have, are presented.

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According to the typical household production model, we predict that increases in married women's wage leads to increases in their labor supply and reductions in the demand for children. However, we recently observe the positive correlation between female labor market participation rates and fertility at the macro level. This contradiction is thought to be caused by the simplification of the model at the micro level, that is, it does not take account of a husband's time allocation in the household although it leads to decreases in the opportunity costs of children. Japanese fertility started to decline since the middle of the 1970s and continued to decrease up until now. So, Japanese Government has strengthened the measures to cope with low fertility issues and began to emphasize the measure to promote men's involvement into housework and childcare in 2002. The purpose of this paper is to empirically examine the effect of a husband's household production activity on a couple's additional desired children after controlling the variables of the typical Becker's model. We used new cross-section data from household survey in Hyogo Prefecture. The empirical results show that a husband's household production activity has a positive effect on a couple's additional desired children, particularly in both the bread-winner household and the household which the wife work as a part-time.

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This study aims to analyze the decision to have fewer children, especially the decision to have no children, using the models in which the influence of childbirth on the women's employment is considered. In previous studies, the change in the state and conditions of women's employment generated by childbirth has been neglected. In contrast,in our models the loss of lifetime income and wage caused by childbirth is considered. The reason for considering this is because in Japan many women quit their jobs upon childbirth, and even if getting jobs again, the conditions are usually worse, so childbirth has a very negative effect on women's employment. Therefore it is indispensable to the analysis of low fertility to consider these influences. Our models follow Becker(1965), but considering that, the cost of a child -budget constraint- is different in other studies. In our models, therefore, there exists a case where parents decide to have no children. Our models show that, as the loss of lifetime income or wage increases, there is a stronger possibility of making the decision to have no children. That is to say, our models prove the very low fertility in Japan more accurately than other models. Our models lead to the conclusion that for the increase in fertility rate it is important to reduce the influence of childbirth on the women's employment.

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The purpose of this study is to simulate the TFR(Total Fertility Rate) of Japan in the future by making simultaneous equation models consisting of a lot of variables, and analyzing the degree of effects of these variables on the TFR. The prominent point in this study, in comparison with some studies which are still performed now, is to take into account the births of a second child or more, and to use the ratio of female workers who engage in part-time work as a variable taking into account the effect of the increase of female "freeters" on lagging their marriageable ages, which is a current problem. I used an OLS to form an estimation and did a deterministic simulation. As a result of estimation about the coefficient and the significant level of female wages reflecting an opportunity cost, the birth of a second child or more was stronger than the birth of a first child, and correlations between the ratio of female workers who engage in part-time work and the ratio of females experiencing first marriage were negative. The period used in simulation was from 2004 to 2019 and six scenarios were prepared. In 2019 the highest case of TFR was 1.34 and the lowest case 0.82. The former is the case where the capacity of day nurseries would have to increase the annual rate to 2 percent and economic growth to 1 percent, and the latter is the case where the capacity of day nurseries would be constant from 2003 and economic growth would increase at an annual rate of 2 percent. In this study it was shown that improvement of the economic environment has a negative effect to decrease births through the increase of female wages and a positive effect to increase births through a fall in the ratio of female workers who engage in part-time work and a rise in the ratio of female first marriages, the former was stronger than the latter. However this result shows that negative correlations between female wages and births may weaken to some extent and the positive effect of improvement of the economic environment may become strong if it is possible to increase child care support as an increase in the capacity of day nurseries to decrease an opportunity cost by policy.

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