In July 2003, Prime Minister Koizumi successfully passed the legislation to dispatch ground SDF units to Iraq in the Diet. His top-down policy process was completely different from Japan's traditional bottom-up system, which Aurelia George Mulgan calls the ‘Un-Westminster System’ in which the bureaucrats in the ministries play a central role with the LDP being the only political power to negotiate with them. Mulgan also argues that the system has not changed despite recent institutional changes. On the contrary, this paper illustrates how Koizumi and his Cabinet took advantage of the strengthened authority of the Cabinet Secretariat to initiate policies, and successfully pushed the controversial national security legislation through LDP decision-making organs and the Diet by gaining support first from the coalition partners, presenting a new style of Westminster system.