Study on the Change of the Proportion of Female Members of the Japanese Parliament from the Perspective of Political Opportunity Structure Theory

This article adapts Political Opportunity Structure theory to explain why Japan’s House of Representatives has never exceeded 12 % women since 1946. I disaggregate opportunity into (1) a formal institutional block – electoral rules, candidate selection, money politics and bureaucratic dominance – and (2) an informal mobilisation thread – women’s education, labour market status, NGO networks and policy expertise. Fuzzy-set QCA and within-case process tracing of four critical junctures (1946, 1989, 2009, 2018) show that abrupt surges in female MPs were triggered by exogenous shocks that temporarily ruptured the institutional block: occupation-imposed large districts, corruption scandals or opposition realignment. Each spike, however, was rapidly neutralised by conservative re-equilibration – reversion to medium-size districts in 1947, re-entrenchment of the 1955 system or the LDP’s 2013–2021 re-centralisation of nomination gate-keeping. Without legal quotas, an incremental “outside-in” strategy is proposed: decentralise nomination rights to prefectural branches, insert mandatory gender-evaluation clauses in cabinet advisory councils, and convert resulting evidence into bills via Japan’s member-initiated legislation route. The study contributes to feminist institutionalism and offers transferable lessons for late-industrialising polities seeking SDG 5.5 without destabilising ruling coalitions.