The is an executive department of the Government of Japan responsible for preserving the peace and independence of Japan, and maintaining the country's national security and the Japan Self-Defense Forces.
The ministry is headed by the Minister of Defense, and is the largest ministry in the Japanese government. The ministry is headquartered in Ichigaya, Shinjuku, Tokyo, and is required by Article 66 of the Constitution to be completely subordinate to civilian authority. Its head has the rank of Minister of State. He is assisted by two vice ministers, one parliamentary and one administrative; and the internal bureaus. The highest figure in the command structure is the Prime Minister, who is responsible directly to the National Diet. The MOD, alongside the Ministry of Foreign Affairs, work on crafting Japanese security policy.
In a national emergency, the Prime Minister is authorized to order the various components of the Japan Self-Defense Forces (JSDF) into action, subject to the consent of the Diet. In times of extreme emergency, that approval might be obtained after the fact.
Their activities are regulated under the .
The Japan Defense Agency (JDA) was established on 1 July 1954 as the central administrative body responsible for Japan's defense and oversight of the Japan Self-Defense Forces (JSDF). Until May 2000 it was headquartered in Akasaka (a site later redeveloped as Tokyo Midtown). Under Article 2 of the Defense Agency Establishment Law, the JDA was initially placed under the authority of the Prime Minister's Office. Following reforms to Japan's central government structure, the agency was placed under the Cabinet Office in 2001.
Within the agency, several internal bureaus played central roles in policymaking and civilian oversight of the JSDF. The Bureau of Defense Policy was responsible for drafting defense policies and programs, determining operational activities, and conducting information gathering and analysis. The Bureau of Finance developed the agency's budget and set spending priorities for both the Defense Agency and the JSDF. The Bureau of Equipment oversaw procurement and equipment management, with subunits corresponding to the ground, maritime, and air services. Major procurement proposals were reviewed by these bureaus before being submitted to the National Diet for approval.
Uniformed JSDF personnel operated alongside these civilian bureaus. The senior uniformed officer was the chairman of the Joint Staff Council, which included the chiefs of staff of the ground, maritime, and air branches. The council's functions included advising the director general of the Defense Agency and planning and executing joint exercises. Each of the three services maintained its own staff offices to manage operations. While military rank determined command structures within each service, all branches were directly responsible to the director general and functioned as coequal bodies with the Joint Staff Council and the staff offices.
This structure was intended to prevent the concentration of military authority seen prior to 1945 under the Imperial General Staff and the Supreme War Council. However, it also limited coordination between services, as formal exchanges among commanders were relatively few. Some senior officers expressed dissatisfaction with the level of authority held by civilian officials in the internal bureaus, many of whom had limited military experience. During the early 1980s the Joint Staff Council was expanded to improve communication between the bureaus and service staff offices, and centralized command and communications systems were developed to link service headquarters with the Defense Agency.
Efforts were also made in the 1980s to clarify command authority during emergencies. The government maintained the principle that military action must remain under civilian control, though concerns were raised that delays in consultation could create operational risks. As a result, vessels of the Japan Maritime Self-Defense Force began carrying live torpedoes and fighter-interceptors were permitted to carry missiles continuously. However, ships were still required to receive specific orders before interdicting intruding vessels. The Defense Agency also considered developing more detailed guidelines for JSDF actions during emergencies.
Cooperation between the JSDF and civilian agencies in contingency planning remained limited. Plans for utilizing civilian aircraft and merchant fleets during crises were underdeveloped, despite the JSDF's relatively limited transport capacity. In 1990 legislation was considered to allow the JSDF to respond to emergency situations not explicitly covered by Article 76 of the .
During this period the JSDF also undertook gradual modernization of its equipment. In 1987 the Defense Agency replaced its communications network, which had relied on telephone lines operated by Nippon Telegraph and Telephone, with a microwave network incorporating satellite-based transmission. Despite these improvements, by 1990 stockpiles of ammunition and maintenance supplies were still considered inadequate.
The Defense Agency was occasionally the target of political violence. In 2004, the agency's headquarters was attacked by a Kakurà Âkyà  cell using improvised mortar barrages.
On 8 June 2006, the Cabinet of Japan endorsed a bill to elevate the to a full cabinet-level under the Cabinet Office. The âÂÂBill for Partial Revision of the Defense Agency Establishment Lawâ was submitted to the National Diet on 9 June 2006.
The bill was approved by the House of Representatives on 30 November 2006. It was subsequently passed by the House of Councillors on 15 December 2006, formally approving the transition from agency to ministry. The legislation received support from the Liberal Democratic Party, Democratic Party of Japan, Komeito, and the People's New Party.
Opposition came from the Japanese Communist Party and the Social Democratic Party, which argued that the move could contribute to Japan becoming involved in future wars. Some countries in the Asia-Pacific region also expressed concern, citing historical memories of Japanese imperial rule during World War II.
The Ministry of Defense was formally established on 9 January 2007, assuming the name and status of a full cabinet ministry. At the same time, the Defense Facilities Administrative Agency was dissolved and integrated into the new ministry.
In 2017, the ministry became embroiled in controversy over operational logs kept by the Japan Ground Self-Defense Force engineering unit deployed to South Sudan as part of the United Nations Mission in South Sudan. The Ministry of Defense initially reported that daily activity logs describing conditions in the conflict zone had been discarded, but it was later revealed that electronic copies had been retained within internal systems, prompting accusations that officials had mishandled or attempted to conceal the records. The controversy intensified political scrutiny of the ministry and contributed to the resignation of Defense Minister Tomomi Inada in July 2017 amid broader criticism of the ministry's handling of documentation related to overseas deployments.
In July 2007, a 21-year-old right-wing activist forced his way through the main gate of the Ministry of Defense complex and threw a Molotov cocktail toward the building before being apprehended.
On 22 October 2025, the Tokyo Metropolitan Police Department began investigating the death of a 60-year-old ministry official who was found unconscious after falling down an elevator shaft inside the Ministry of Defense building.
is an annual white paper published by Japan's Ministry of Defense. The report provides a comprehensive overview of Japan's defense policy, national security environment, and activities of the Self-Defense Forces. The publication is translated from Japanese into English and Chinese and made publicly available on the ministry's website. Digital archives of the white paper are also provided online, with available issues dating back to 2014.
The Ministers in the Ministry of Defense are as follows:
The Senior Advisers to the Minister of Defense are senior policy advisers to the Minister of Defense.
The Special Advisers to the Minister of Defense are special policy advisers to the Minister of Defense.
The Administrative Vice-Minister of Defense, the senior civil-servant at the Ministry of Defense, has the role of coordinating the affairs of the Ministry and of supervising the Ministry's bureaus and organs.
The Chief of Staff, Joint Staff is the highest-ranking military officer of the Japan Self-Defense Forces, and the senior military adviser to the Minister of Defense and the Japanese Government. He is supported by the Vice Chief of Staff, Joint Staff. He is appointed by the Minister of Defense, approved by the Cabinet.
The Ministry of Defense includes a number of organizations as of 2024: