Japan's first openly gay male lawmaker said on Tuesday he believed the country would legalize same-sex marriage, months after Taiwan became the first place in Asia to allow gay unions.

Taiga Ishikawa, 45, was elected to the Diet's Upper House on Sunday, on a platform calling for marriage equality, with the main opposition Constitutional Democratic Party, also the party of Japan's first openly LGBT+ lawmaker, elected in 2013.

"Since the early 2000s, the issue of same-sex marriage has progressed leaps and bounds," Ishikawa told the Thomson Reuters Foundation by phone on Tuesday.

Same-sex marriage is illegal and Prime Minister Shinzo Abe has opposed efforts to legalize it. However, a solid victory for Abe's ruling bloc in Sunday's Upper House election has led some LGBT+ rights advocates to question whether reforms will be achieved soon.

Japan's first openly lesbian lawmaker, Kanako Otsuji, 44, helped table a marriage equality bill in June but the ruling Liberal Democratic Party and its coalition party, Komeito, have declined to debate it. Read more via Asahi