According to Governor Yuriko Koike, Japan's capital Tokyo, the country's largest population center, plans to introduce the legal instrument of same-sex partnership in the coming fiscal year.
With the change, Koike wants to promote an understanding of sexual diversity in society.
The details are not yet clear, but same-sex partnership will not create full legal equality with marriage between a man and a woman.
Dozens of smaller municipalities in Japan have already moved in terms of same-sex partnerships in recent years.
In the group of seven large democratic industrialized countries, only Japan does not accept same-sex marriages.
In the post-war constitution, which has never been changed since the end of World War II, marriage is described as a partnership of both sexes.
For the first time last year, a court in Sapporo ruled that the ban on same-sex marriage was unconstitutional.
Surveys show that the majority of the population would have no objection to same-sex marriage.
But the conservative Liberal Democrats, even under the new Prime Minister Fumio Kishida, are not prepared to initiate a corresponding change in the law.