In Japan, the trends toward gender egalitarianism, which proceeded after the war, have stalled, and some recent studies find the reversal turning downward, in the recent cohort or period. To understand the longitudinal change, we focus on the issue of how and to what extent the change in social status composition contributes to the change in gender role attitudes, and conduct a decomposition analysis of the period, cohort, and composition effects. We also conduct a mediation analysis investigating the relationships among cohort, social status variables, and gender role attitude using SSM survey data for 1985, 1995, 2005, and 2015. The findings reveal the significant indirect effects of the cohort on gender role attitudes mediated by social status variables. Among women, in younger cohorts, the composition changes, including the popularization of higher education, or growth of professional and managerial workers, contribute to the increases in gender egalitarianism. Among men, the increase in regular employment for their mothers and change in education and job status for their wives are significant contributors. These results highlight a value change through multiple ways that the composition changes of various social statuses such as education, work, and family, liberalized gender beliefs with gender differences, while in some cases, were influenced by the significant othersʼ status. Besides, our results clarify the mechanism behind the recent reversal in gender attitudes as follows. Although in younger postwar cohorts, there are no significant changes in gender role attitudes（total effects）, when we control for the above indirect effects or the increase in gender egalitarianism caused by the composition change, we find the direct cohort effect that younger cohorts are coming to believe in a traditional gender role among women.