Supreme Court Chief Justice Yukihiko Imasaki has vowed to handle "appropriately and speedily" cases in which requests for retrial are made after guilty verdicts were finalized.

"There have not been many requests for retrial, so it is not easy to share and accumulate experiences," he told a news conference ahead of the country's Constitution Day on Saturday.

Imasaki noted that criminal judges have discussed issues such as trials tending to be prolonged at the Legal Training and Research Institute. "It is important to share (such experiences) widely," he said.

On same-sex marriage, Imasaki said, "It is necessary to understand the reality in society, and making balanced decisions is also important." Five high courts in Japan have ruled that Civil Code and family registration law provisions that limit marriage to a man and a woman are unconstitutional.