Junko Sakai, a stylish 37-year-old sipping fresh grapefruit juice at a hip center city cafe, insisted that she did not mean to create a furor when she wrote her blockbuster book about the little-told lives of single Japanese women. Instead, Sakai said, she was merely out "to clear up a few misconceptions."

But in a male-dominated culture in which a woman's success has long been based on her ability to bag a good man, Sakai's book is a rallying cry for the modern single woman.

"Marriage is not an institution that fits everyone," said Sakai, whose book, "The Howl of the Loser Dogs," describes the advances of women who were once considered "losers" for not getting married. "Modern Japanese women who have jobs . . . don't want to spend their lives cooking and cleaning for traditional-thinking Japanese men. Basically, we like to say we're just too beautiful and smart to marry. . . . But the truth is, we are single, and we shouldn't hide from that word."

Japan is undergoing a major redefinition of gender roles as women enter the workforce in record numbers, according to analysts. The result is the rise of financially independent Japanese women. And when it comes to marriage, increasingly, they are just saying no to men.

Today, some luxury condos around Tokyo are being marketed strictly to successful women. The Tokyo Stock Exchange recently offered a workshop aimed at luring well-off single women to invest. And with the wedding ring business in decline, Camellia Diamonds, a large Japanese jewelry firm, has begun running advertisements in which a single woman boasts she no longer needs a man to treat herself to gems.

"There's no question the Japanese woman is changing, coming into the center from the periphery of society," said Eisuke Sakakibara, an economist at Tokyo's Keio University. "They have discovered they can stay single, spend money more freely, and have fun without having to take on the traditional responsibility of taking care of a man. With those options available, they are asking themselves, 'Why get married?'' "

The percentage of singles in Japan has already surpassed the percentage in other industrialized nations, including the United States, where the ranks of the non-married are already inflated by far higher divorce rates than in Japan. In 2003, 54 percent of Japanese women in their late twenties were single, compared with only 24 percent in 1980.

About 43 percent of Japanese men in their early thirties are unmarried, double the rate in 1980. By 2020, almost 30 percent of Japanese households will be headed by singles. In Tokyo, the world's largest urban area, the number is more than 40 percent, according to government statistics.

The decline in marriage, in part, is a result of the protracted economic slump that began in Japan in the early 1990s, when men were less confident about their ability to support families and were more reluctant to marry, according to analysts.

But academics mostly point to a shift in the lifestyle choices of urban Japanese women. Even during the recession, Japanese women were heavily courted by employers initially seeking cheaper sources of labor in the service sector, which was not hit as hard as other parts of the economy by the recession. Although Japanese women still lag far behind women in other industrialized countries in terms of representation in the upper echelons of business and politics, they are well-established in the labor market as Japan's economy recovers. Last year, for instance, the percentage of women in the workforce hit a high of 40.8 percent -- compared with 35.9 in 1985, during the days of Japan's bubble economy.

Japanese women have often been herded into marriage out of tradition, obligation and, ultimately, financial necessity. But now their access to the workplace is being viewed as a breakthrough in women's rights.

A growing minority of single women have even opted to stop waiting for marriage to build their dream houses. Nagako Motomiya, 49, a senior administrator with the City of Tokyo, hired a Kyoto-based architect who published a book about homes for singles to build a $400,000 one-bedroom, three-level house in west Tokyo. With delicate and pricey furniture and a floor-to-ceiling "moon-gazing window" for relaxing evenings at home, it is tailor-made to her lifestyle.

Only a decade ago, such a move would have been seen by many in Japan as shockingly self-indulgent for a woman. But the country, Motomiya said, is changing.

"I haven't given up yet on marriage. . . . But in this day and age, you can live comfortably as a single woman in Japan," she said.

"In the past, it was difficult for women to have the income to live on their own," she said. "If you weren't married, you got that look from people and your parents. But not any more, not at all."

The resulting change is also being cited as a major factor for the birthrate decline of the past few decades. With women giving birth to an average of 1.29 children -- among the lowest rates in the world -- Japan's population is expected to peak at an estimated 128 million within the next two years. After that, the Japanese population is projected to decrease -- dropping to 120 million by 2026 and to 100 million by 2050, according to government statistics.

That raises critical questions about whether Japan -- traditionally adverse to immigration -- will have enough workers to run the world's second-largest economy. In addition, with fewer workers paying into the pension system and Japan's population graying -- on average, the Japanese live longer than any other people on earth, with a lifespan of 85.33 years for women and 78.36 for men -- the national pension system here is on the verge of bankruptcy.

Some Japanese men, including political leaders, have criticized single women who refuse to retain their traditional roles in the home. Yoshiro Mori, Japan's former prime minister, insisted angrily last year that women who did not give birth should not receive pensions.

"Welfare is supposed to take care of and reward those women who have lots of children," he said in a speech. "It is truly strange to say that we have to use tax money to take care of women who don't even give birth once, who grow old living their lives selfishly and singing the praises of freedom."

Some Japanese bachelors are getting desperate. After 10 failed attempts to find a bride through a matchmaking service, Masayuki Kado, 39, enrolled in a new bridegroom school in Nagoya, Japan's fourth-largest city.

Kado, a solar panel researcher, endured lessons in witty conversation, clothing coordination and good grooming habits. But in the real world, Kado said his biggest hurdle had little to do with clothes or charm. "It's difficult even after marriage. Women today no longer want to stay home," he said. "But I still want to come home after work and see my wife greeting me at the front door saying, 'Welcome home, honey.' "

Many single women here say that such traditional attitudes have kept them from marrying in the first place.

"Single women in Japan generally do want to marry -- or at least I did, and I still do," said a 40-year-old successful female executive who spoke on the condition of anonymity to preserve her privacy. Chatting at a Tokyo Starbucks, she said she had turned down a promising suitor because he expected her to quit her job to be a full-time wife and mother.

Men "need to update the way they think of women," she said.

Special correspondents Sachiko Sakamaki and Akiko Yamamoto contributed to this report.

Author Junko Sakai wrote blockbuster on single women.Nagako Motomiya, a senior administrator with the City of Tokyo, said she hasn't "given up yet on marriage. . . . But in this day and age, you can live comfortably as a single woman in Japan."