Social dance comes out of the closet in Japan, transforming from sleaze to a healthy sport--and, thanks to a hit film, attracting throngs of new fans.

It’s 7:30 p.m. and the dark-suited Japanese business executives are beginning to trudge into the room. From the depths of their bags and briefcases, they pull out--suede-soled shoes. They don them and shrug off their jackets. Then, with steely concentration, they begin an intense training to help them achieve their latest competitive goal.

But this session is a graceful recital of movement. Glide, thrust, turn; slow, slow, quick. The men twist their hips, point their toes and gently curve their hands as they try to perfect a pastime enjoying a new boom here: the art of ballroom dance.

Here is building inspector Tsuyoshi Hakuta and graphic designer Hiroshi Muraishi twirling invisible partners, checking their forms in the reflection of the windows in this converted meeting room of Tokyo University. Ten years ago, they would have kept their hobby a secret.

That is because social dance, as it is called here, has long stirred lecherous images of furtive groping in darkened halls; the government has regulated it under the Act to Control Businesses Affecting Public Morals since the Meiji Period in the 19th century.

“My colleagues don’t understand dance at all,” said Muraishi, 62, who has lost 15 pounds and made friends since starting dance three years ago. “They think I’m doing it just to pick up women.”

But social dance has began shedding its image of sleaze to become a healthy sport--and thanks to a hit film, it is attracting throngs of new fans. “Shall We Dance?” by Masayuki Suo, one of Japan’s hottest filmmakers, became a top box-office hit, second only to “Seven” since its Jan. 27 release--a rare feat in this market, dominated by Hollywood. So far, the film has pulled in $24 million in box-office receipts, a sum fast approaching Juzo Itami’s Japanese mega-hit “A Taxing Woman.”

The dance story strikes familiar chords in most every Japanese: A worn-down, burned-out businessman feels an inner void now that he’s fulfilled the standard social expectations of marriage, family and home ownership. As he rides the crowded commuter train home, the protagonist, Shohei (Koji Yakusho), sees a beautiful woman, Mei (Tamiyo Kusakari, one of Japan’s top ballerinas), standing in front of the window of a dance studio. He starts taking lessons to meet her--but ends up falling in love with dance itself.

In the process, he is transformed from a working drone to a man of dance and dreams.

Dance instructor Toshio Watari says his students have increased tenfold since the film’s release.

Although ballroom dance has waxed and waned in popularity here since it was first introduced in the 19th century, the film has helped spread its appeal. No longer an elitist form, as imported from Europe, this dance has gone casual, with people today holding parties with canned juice and peanuts, “throwing their bodies around like an octopus,” said Hitoshi Nakagawa of Dance View magazine.

Women are flocking to studios in twirly skirts and shimmering dancing shoes; many use the competitions to attire themselves in eye-stopping fantasy wear of plunging necklines, ostrich feathers and glittering rhinestones they would dare not wear anywhere else.

But the most conspicuous new converts are middle-aged businessmen, known here as salarymen, with time on their hands as a five-year recession has cut back overtime hours.

At a recent film showing in the fashionable Ginza district of Tokyo, Sakae Nakagawa, a 43-year-old cook who works from 7 a.m. to 10 p.m., said he wants something to fill his life, but finds the standard stressbusters of sake and karaoke “boring.”

Shall he dance? Nakagawa isn’t sure, but he’s seen the film twice and seems ready to take the plunge. “I want to try something new,” he said. “I want to invigorate myself.”

At first glance, ballroom dance might seem an uneasy cultural fit here in a society of formal bows rather than touchy hugs, in a place where a poker face is the norm.

But new convert Kenji Takada said changing mores--lovers now casually hold hands and even kiss in public--have made today’s Japan more receptive to the intimate customs of European dance. Still, a generation gap is evident: Building inspector Hakuta, 44, said it took him two years to get beyond his balking at body contact; Takada, 25, says it was no big deal from Day One.

In an interview in Dance Fan magazine, film director Suo--whose previous two films spoofed the traditional worlds of sumo and Buddhism--said he chose the dance theme because Japan has “perfectly adapted” the European tradition.

Unlike the open competitions that characterize ballroom dance in such famed locales as Blackpool, England, the Japanese have created a 12-tiered ranking system that reflects their love of challenge and methodical, step-by-step improvement, said dance instructor Tsuyoshi Akimoto.

Japan’s corporate warriors are finding ways to parlay their dance lessons into improved business performance. Shibata, for instance, says he can now twist and turn his opponent in negotiations, just as he nimbly leads his wife in dance.

And two entrepreneurs have produced a spine-straightening contraption that hooks onto the back and sold 5,000 sets--each $90--in the past six years.

But Suo, who aims to release the film this year with English subtitles, says he wanted to show that dance needs no other motive than simple pleasure. “I made the film to show young people how magnificent social dance is,” he said, “and wishing that middle-aged couples would feel more relaxed about it and use it to enrich their married lives.”*

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Chiaki Kitada of The Times’ bureau contributed to this report.