The Supreme Court of Japan (最高裁判所, Saikō-Saibansho; called 最高裁, Saikō-Sai for short), located in Hayabusachō, Chiyoda, Tokyo, is the highest court in Japan. It has ultimate judicial authority to interpret the Japanese constitution and decide questions of national law. It has the power of judicial review, which allows it to determine the constitutionality of any law or official act.

The modern Supreme Court was established in Article 81 of the Constitution of Japan in 1947. There was some debate among the members of the SCAP legal officers who drafted the constitution and in the Imperial Diet meeting of 1946 over the extent of the power of the judiciary, but it was overshadowed by other major questions about popular sovereignty, the role of the emperor, and the renunciation of war. Although the ratified wording in Article 81 states that the court possesses the power of judicial review, a part of the court's early history involved clarifying the extent of this power. In 1948, the court declared that the constitution meant to establish the type of judicial review that was practiced in the United States. In 1952, the power, as the Court held, was clarified to apply only in cases with a concrete case.

In the 1960s and 1970s, the Supreme Court experienced a "judicial crisis" between older judges and generally younger, more liberal judges. For example, there was controversy when some judges in lower courts were seen as frustrating the implementation of ordinances that would limit anti-government demonstrations. In 1971, the Supreme Court deliberately did not reappoint assistant judge Yasauaki Miyamoto, who participated in a legal organization associated with left-wing ideological leanings. This "Miyamoto Affair" resulted in significant media coverage and protest by other judges. Since then, no judge has failed to be reappointed. Ultimately, the court was reshaped during the 1960s and 1970s to become more conservative, with more representation among the justices from lifetime government employees, which resulted in decisions that tended to limit free expression and public demonstration.

Article 81 of the Constitution of Japan defines the Supreme Court as a court of last resort and allows it to conduct judicial review through "the power to determine the constitutionality of any law, order, regulation or official act". In its first role as a court of last resort, the Supreme Court hears civil, administrative, and criminal cases appealed from lower courts. This responsibility and the inability to apply discretion in the appeals it hears results in civil and criminal appeals being a significant majority of its caseload. In its second role, the Supreme Court can exercise its power of judicial review when a concrete legal dispute involving a violation or misinterpretation of the constitution is appealed.

The Supreme Court also manages the operation, budget, and personnel of all of Japan's courts. Decisions are made by a regular Conference of the Justices in the Supreme Court and implemented by the Administration Bureau of the Supreme Court. The Chief Justice of the Supreme Court, through the office of the General Secretariat, also has extensive control over judicial personnel, including judges. This includes the ability to determine posts of judges, which has a significant impact on their careers and advancement opportunities. The Supreme Court also oversees the Legal Research and Training Institute, which prospective legal professionals who have passed the National Bar Examination are required to attend to receive practical training.

Although the Supreme Court has established the power to strike down legislation that is unconstitutional, it has used this power extremely infrequently. By a simple numerical count, the Supreme Court struck down only eight laws on constitutional grounds over a period of six decades, during which the German Federal Constitutional Court struck down over 600, the United States Supreme Court over 900, and the Indian Supreme Court over 2,600. Furthermore, in at least one case where a constitutional violation was found, regarding election district apportionment, the court has been unable to achieve compliance with its ruling.

Observers have proposed several possible reasons for this. One critical view is that the membership of the Supreme Court is influenced by the political dominance of the LDP, and therefore is less likely to challenge legislation produced by aligned politicians in the National Diet. There could also be the desire to maintain good relationships with judges in the Ministry of Justice or other departments. Another critical view is that the court functions like a bureaucracy, with a conservative leadership promoting like-minded judges that are less likely to make significant decisions. A historical perspective argues that the early judges were influenced by a Meiji Constitution and German jurisprudence tradition that did not allow striking down unconstitutional legislation, and that over time this expectation resulted in a reluctance to act in politically sensitive cases to maintain judicial independence.

One more favorable explanation is the role of the Cabinet Legislation Bureau in the legal ecosystem. The bureau is composed of senior bureaucrats and a minority of judges, some of whom go on to join the Supreme Court. It has the responsibility of thoroughly investigating government legislation to avoid constitutional flaws. Proponents of this view argue that this process prevents the need for the Supreme Court to frequently strike down legislation, as violations of the constitution are removed during the legislative phase.