After the collapse of the Cold War system, Japan became more active in contributing to international peace and security. Especially under the Koizumi administration, Japan successfully passed major pieces of national security legislation, such as the 2001 Anti-Terrorism and the 2003 Iraq Special Measure Laws, in a timely manner. A changing international security environment in the Cold War transformed Japan's media and public opinion to a more realistic one, which supported Koizumi's active national security policy and changed the dynamics of party politics. In order to prove this, this study first explores the influence of the Japanese media, especially the press. Next, it presents the opinion of major newspapers and the public on individual national security issues. Finally, it analyzes the press's influence on public over the issue of constitutional revision.