The ruling dealt a blow to gay couples and rights activists, after another district court in Sapporo ruled in 2021 that the failure to recognize same-sex marriage was "unconstitutional".

Japan's constitution defines marriage as one between "both sexes".

It is the only country in the G7 group of developed nations that doesn't allow people of the same gender to marry.

The Osaka case was only the second of its kind to be heard in the country, where conservative attitudes toward homosexuality remain.

In addition to rejecting their claim that being unable to marry was unconstitutional, the court also dismissed demands for 1 million yen ($7,414; £6,058) in damages for each couple who argued they had suffered "unjust discrimination" by not being allowed to marry.

The plaintiffs plan to appeal against the decision, Kyodo news agency reports.

Japan's constitution, put in place after the end of World War Two, defines marriage as one of "mutual consent between both sexes".

Under the current rules, same-sex couples are not allowed to legally marry, can't inherit their partner's assets, and have no parental rights over their partner's children.

Though partnership certificates issued by some individual municipalities help same-sex couples to rent a place together and have hospital visitation rights, they do not grant them the full legal rights enjoyed by heterosexual couples.

Activists also say conservative attitudes towards homosexuality mean many LGBTQ Japanese still do not dare to come out to their friends and family.