BEIJING — A judge on Wednesday ruled against a gay couple who had sought the right to marry, in China’s first court case addressing same-sex unions.

Sun Wenlin and Hu Mingliang had filed a lawsuit against a civil affairs bureau in Changsha, Hunan province, after the office refused to grant them the right to marry when they tried to register in June.

A district court accepted the case early this year, the first time a Chinese court had agreed to hear such a lawsuit. The court held a hearing Wednesday, and the judge ruled a few hours later. News of the ruling began circulating on social media shortly afterward.

Sun said in an interview that he and Hu planned to appeal. They have 15 days, according to Chinese law.

Sun said he had argued that he and Hu should be allowed to marry since the law did not explicitly ban same-sex marriage.

“We said this at the hearing, but they just kept repeating articles that mention ‘a man and a woman,’ ’’ he said, referring to the civil affairs bureau.

The bureau cited three articles from China’s marriage law and two from the official marriage registration regulation, he said, with four mentioning “a man and a woman’’ and one stating a civil affairs bureau may refuse applications if a couple is not qualified to marry.

“But the fact that marriage between a man and a woman is legal does not suggest that marriage between two men is illegal,’’ he said. “This is illogical. I asked them to name one article that explicitly bans marriage between two men, but they never answered my question directly.’’

The case has galvanized some advocates in China. Photographs and video taken in Changsha showed many people gathering outside the courthouse to support Sun and Hu.

The case has also received considerable attention on Chinese social media as a test of the authorities’ attitude toward same-sex marriage. Internet users said that although the result was unsurprising, the couple had achieved a big step.

“In this era, being able to knock open the court’s door is already a victory. Keep going,’’ a user with the handle Garden on the Roof wrote on Weibo, China’s equivalent of Twitter.

Sun said he and Hu were disappointed. “But after seeing so many people are paying attention to this case, we feel very hopeful,’’ he added.

Some Chinese state-run news organizations had reported on the case over the winter, including the English-language edition of Global Times. The Twitter account of People’s Daily, the official newspaper of the Communist Party, posted news of the ruling Wednesday, using a photo of the couple holding hands while crossing a street.

Sun told his family he is gay when he was 14 and has been a vocal supporter of gay rights. For eight months, he ran a teahouse in southern Changsha where he gave weekly talks on sexuality and identity.

Hu, 37, a security guard, met Sun through a chat group in 2014. They said they did not spend a day apart after their first meeting. They tried to register their marriage on the first anniversary of their meeting.