Parliamentary reform between 1945 and 1947 was one of the key policies implemented in Japan during the Allied occupation. It brought a fundamental change to the institutional arrangement of the Japanese legislature. This article finds that it was truly a by-product of the U.S. congressional reform around that time. The newly established National Diet of Japan bore a significant resemblance to the U.S. Congress reorganized by the Legislative Reorganization Act of 1946. Some novel institutions proposed by congressional reformers were struck down at home but survived on the opposite side of the world. Although the main content of the reform was not optimal for Japan, it was the best choice from the subjective view of GHQ/SCAP in Tokyo. The author also contends that GHQ/SCAP expected the House of Councillors to be an obstacle to the democratization of Japan. Thus it was rational for GHQ/SCAP to provide the House of Representatives with veto power that would infringe the autonomy of the upper chamber.