Aki is a pretty twentysomething shop worker who lives with her parents, has a steady boyfriend and wants to travel to Europe. Little apparently marks her out of the ordinary except that once a week for the last two years she has been visiting a club to have sex with total strangers. "Not everyone," she stresses. "Only about one in five of the men I meet here."

Located above a convenience store in one of central Tokyo's grey business blocks, the nondescript club, called Dream, seems to mirror the ordinariness of the clientele, mostly curious refugees from the city's corporate army of office workers and salary men. Not a pink neon sign nor a burly bouncer in sight, this is lechery at its most antiseptic.

Less burdened by Western ideas of sin and shame about pleasures of the flesh, Japan's erotic culture continues to blossom even as its economic fortunes fade. Along with garden variety massage parlours, strip joints and porn shops, most cities offer a smorgasbord of exotica for the jaded - usually male - palate. Kabukura cabaret clubs, where clients pay to drink with, and touch, the staff, and fetish clubs called imekura, where fantasies such as molesting strangers on trains are acted out, are just the most recent additions. It is tempting to speculate on the relationship between Japan's economic slump and its apparently ever-expanding sex industry, whose total earnings, claimed the Far Eastern Economic Review recently, equal the nation's defence budget. Certainly the owner of Dream has his own theories.

"People are stressed out and depressed, and they find it hard to meet other folk," he says. "They come here to break out of their straightjacket lives and leave with a smile on their face."

Dream was one of the first of dozens of so-called Couple Kissaten (literally "couples coffee shops") that have sprung up around the country in the last three years. A former office worker, the owner explains in the tone of a faintly bored furniture salesman, how the place operates.

Punters find a small waiting area with a bar and a notice board covered with profiles and photographs of people who have rented one of 19 tiny rooms on the premises. Single men are charged a 5,000 yen (£35.50) one-off membership fee plus 4,000 yen (about £28.50) an hour. Women and couples go free. The profiles list the age, body-type and sexual interests of each person at the top, with more detailed information further down. A section indicates whether they are interested in sharing, swapping or three-way sex. Many, it seems, are.

"I tried it once with a couple," says Nobu, a 27-year-old shop assistant who was brought along by her younger sister six months ago. "It was a bit embarrassing at first, but fun." Nobu comes to the club twice a week and likes it because it is safe and clean. She can't quite remember how many men she has had sex with but reckons "about 40". She talks frankly about her sexual preferences. I look in vain for signs of reddening cheeks while she chirps away into my microphone before realising I'm blushing myself.

Forget all your usually correct theories about sexual services exploiting women - at Dream, at least, female customers seem to get the better deal.

Most visit after hearing about it from a friend and return after being reassured by the brightly lit interior and female staff. If they don't like the vibe from one punter, they can leave the room and try another. All the women I talked to have boyfriends who know nothing about their visits.

Single men must pay, wait, and learn how to talk. Kan is a 28-year-old mobile-phone salesman who has been coming weekly for four years. Although slim, sharp featured and well dressed, he claims he seldom gets lucky. "You have to be good at chatting and I'm useless," he says. "Your face is only part of the game."

He sometimes pays for up to four hours before giving up. I mentally calculate the cost of this weekly outlay times four years. If he really has to pay for sex, wouldn't it be better to go to a prostitute? "They're professionals," he says. "These women are just ordinary people, like me."

The owner says business is good and his punters include doctors, lawyers, lots of foreigners and even police. His oldest visitor was 71, but little surprises him since a well known politician from the Democratic Party of Japan came through the door. He knows Ireland and England fans will be coming next year for the World Cup. "An Irish woman came last year," he adds. "She had a great time."