TOKYO (AFP) - Japan was stung by its third political scandal in a week after the country's new industry minister - whose predecessor resigned in disgrace over misspending - admitted that his underlings had spent office cash at a sex bar.

The new revelations on Thursday deal another serious blow to the administration of Prime Minister Shinzo Abe which was already facing a public backlash over its bid to turn Japan's shuttered nuclear reactors back on and its stalling plans to revive the economy.

As news of the sex-bar scandal broke, industry minister Yoichi Miyazawa, a Harvard graduate and former top bureaucrat in the finance ministry, distanced himself from the affair, saying he wasn't present at the sex club in the city of Hiroshima.

But he acknowledged that some staff at his political office had billed 18,230 yen (S$216) as entertainment expenses during a visit in September 2010, Jiji Press news agency said.

"I came to know of that through a media report, and it was true," Miyazawa told reporters in Tokyo on Thursday.

"It is also true that I myself was not there," he added.

The venue's shows depict women being tied up with ropes, and male customers are allowed to take part in the show by whipping them, according to blog posts written by club visitors.

It was not immediately clear if Miyazawa - a nephew of late prime minister Kiichi Miyazawa and a cousin of Foreign Minister Fumio Kishida - would step down.

"(Miyazawa) will handle the case properly," said Chief Cabinet Secretary Yohishide Suga, the government's top spokesman, in the only comment from Abe's ruling Liberal Democratic Party.

On Tuesday, Miyazawa was tapped to replace industry minister Yuko Obuchi, who stepped down over claims she misspent political funds, while Justice Minister Midori Matsushima also quit after days of allegations that she had misspent money in what opponents insisted was an attempt to buy votes.

The double resignations earlier this week marked the first significant problem for Abe since he swept to power in December 2012, ending years of fragile governments that swapped prime ministers on an annual basis.

They were also a blow to Abe's proclaimed bid to boost the profile of working women in Japan, while commentators said his administration could be in trouble if their replacements did not have solid reputations.

The industry ministry oversees the energy sector and is the face for Tokyo's attempts to convince a sceptical public on the safety of re-starting stalled nuclear power plants - more than three years after the Fukushima atomic crisis.

All of Japan's 48 operational nuclear reactors are currently switched off. But Tokyo has been pushing to return to a source that once supplied more than one-quarter of Japan's energy, as heavy energy import bills weigh on the country's trade balance.

Meanwhile, Abe's bid to kickstart Japan's long-laggard economy has stumbled after his government raised sales taxes in April to help pay down a massive national debt.

Abe himself was forced to resign in 2007, only a year into his first premiership after several of his ministers were hammered by political scandals.

Then farm minister Toshikatsu Matsuoka, one of Abe's cabinet members, hanged himself in 2007 after becoming embroiled in a scandal over political spending.

Former state minister for regulatory reform Genichiro Sata, another key Abe lieutenant, stepped down over questions about his political spending.

Last year, Sata resigned from a party post after a magazine said he had gone on paid dates with a female university student. The publication ran pictures of him emerging from a love hotel with the woman.