一般分析日本的防衛政策有二個面向：一是從日本周邊的安全保障環境或美國的亞太戰略來分析日本防衛政策的變化，二是從日本國內的執政黨、首相的政策意圖，甚或朝野政黨的對立來說明防衛政策的決定。本文則嘗試以內閣法制局的角色為中心，說明其在防衛政策中的影響力。戰後日本再度武裝與簽訂美日安全保障條約時，規定不以行使武力做為解決國際紛爭的手段、不承認交戰權、不保持陸海空戰力的日本國憲法已經公布施行。換言之，日本在建構防衛力量與美日安全保障體制之際，已經面臨憲法的制約，出現是否違憲的爭議。在是否違憲的爭議中，內閣法制局實際上扮演不容忽視的角色。內閣法治局長官是特別職的公務員，由內閣總理大臣任免之，是內閣的一員，具有支援內閣政策的義務；但是同時，內閣法制局長官為內閣的法律顧問，慣例上不因新內閣的成立而更替，具有政治上的中立性與獨立性。因此，當日本的防衛政策出現重大變革時，內閣法制局便位居關鍵性的地位。本文首先說明何謂內閣法制局，其次分析內閣法制局的權威性，接著則以集體自衛權行使的放寬的為例，說明內閣法制局的政治性角色。

Two perspectives are generally used when analyzing defense policies adopted by Japan, in which the first investigates changes in Japan's defense policies using secured environments surrounding Japan or Asia-Pacific strategies employed by the United States, whereas the second explains defense policy-related decisions using Japan's ruling party, prime minister's intentions behind such policies, or oppositions between the ruling and opposition parties. In this study, we investigated the role and impact of Japan's Cabinet Legislation Bureau on Japan's defense policies. After the Second World War, Japan changed its military composition and signed the Treaty of Mutual Cooperation and Security with the United States, stipulating that military forces not be used as a means of settling international disputes, that the right of belligerency be abolished, and that Japan withdraw its military forces (i.e., ground forces, navy, and air force), all of which have been promulgated in and implemented as the Constitution of Japan. In other words, Japan’s building of defense forces and US-Japan security systems are controlled by Japan constitutional laws, and the building of such forces in Japan may result in disputes concerning violations of such laws. When this occurs, the Cabinet Legislation Bureau plays a crucial role in resolving such disputes. Director-general of the Cabinet Legislation is a civil servant with special duties. He/she is a member of the cabinet who is appointed and dismissed by the prime minister and who has obligations to support Cabinet policies. Concurrently, the Cabinet Legislation director-general serves as the legal counsel of the Cabinet and normally does not change when the Cabinet changes; he/she is thus politically independent and neutral. Therefore, the Cabinet Legislation Bureau plays a critical role when significant changes are made to Japan's defense policies. In this study, we first provided a description of Japan's Cabinet Legislation Bureau. Next, we analyzed the authority of the Cabinet Legislation Bureau. Finally, we explained the political role of the Cabinet Legislation Bureau by examining the relaxation of Japan's policy regarding exercising the right of collective self-defense.