The aim of this paper is to investigate the relationship between wives' socioeconomic contributions to the family and income differentials between households using data from the 1995 Social Stratification and Social Mobility (SSM) Survey. We compared the median income for husband/household income within the same (husbands') occupational group, and for wife/husband/household income among different occupational groups.
　The findings are as follows: (1) the median income of husbands with working wives is lower than that of husband with non-working wives ("Douglas-Arisawa's Law"; (2) The wives' labor force-participation makes the household income with working-wives makes larger than that of income with non-working wives; (3) The addition of wives' incomes to the family provides a functional substitute for the rise in earnings that might result from upward occupational mobility of the husband. These findings coincide with those of a study previously conducted in America. Other outstanding findings are as follows: (4) There is a large disparity between the income of households with professional or managerial husbands and that of others; (5) For husband-wife families in their 50s, the labor-force participation of wives equalizes the income differentials between households, whereas in younger families, some women married to high-earning men have a propensity to work, which increases the income differentials. That is, "Douglas-Arisawa's Law" has gradually weakened. Among the younger generation, wives' labor-force participation has an enlarging effect on the income differential within households. Hence, if wives' labor-force participation increases and other conditions are constant, income inequality may increase.
　The difference in income between wife and husband is large. However, this empirical evidence suggests the importance of income inequality among women.