The composition of the Supreme Court is defined by the 1947 Judiciary Act.
The Supreme Court is composed of a Chief Justice and fourteen other Justices.
These Justices are divided into three Petty Benches of five, which adjudicate most appeals.
Questions of constitutional interpretation are adjudicated by the Grand Bench of all fifteen Justices, of which nine is needed for a quorum.

Associate Justices of the Supreme Court are both selected and appointed by the Cabinet of Japan but the Chief Justice differs in being appointed by the Emperor of Japan.
 Justices are required to be over the age of forty and possess an extensive knowledge of the law.
After appointment, in the next general election a judge can be dismissed if a majority favors dismissal, but a Supreme Court Justice has never been dismissed in this way.
Although a public review is stipulated to occur every ten years after appointment, since Justices are generally appointed at age sixty or older and must retire at age seventy, there are "effectively no second reviews."

Particular to the Supreme Court of Japan is the uncodified custom of having seats of the court be allocated to different legal professions: career judges, private attorneys, prosecutors, academics and bureaucrats.
The numbers for each group have been subject to some variation, but overall have been remarkably stable since the court's inception.
The composition of the Supreme Court is defined by the 1947 Judiciary Act. The Supreme Court is composed of a Chief Justice and fourteen other Justices. These Justices are divided into three Petty Benches of five, which adjudicate most appeals. Questions of constitutional interpretation are adjudicated by the Grand Bench of all fifteen Justices, of which nine is needed for a quorum.
Associate Justices of the Supreme Court are both selected and appointed by the Cabinet of Japan but the Chief Justice differs in being appointed by the Emperor of Japan.  Justices are required to be over the age of forty and possess an extensive knowledge of the law. After appointment, in the next general election a judge can be dismissed if a majority favors dismissal, but a Supreme Court Justice has never been dismissed in this way. Although a public review is stipulated to occur every ten years after appointment, since Justices are generally appointed at age sixty or older and must retire at age seventy, there are "effectively no second reviews."
Particular to the Supreme Court of Japan is the uncodified custom of having seats of the court be allocated to different legal professions: career judges, private attorneys, prosecutors, academics and bureaucrats. The numbers for each group have been subject to some variation, but overall have been remarkably stable since the court's inception.
Supreme Court of Japan