TOKYO, SEPT. 2 -- The Japanese Supreme Court today issued a landmark ruling that opens the door to "no-fault" divorces for the first time in this traditional country that has long attached a social stigma to divorce.

The court said that a 75-year-old Tokyo businessman, who first filed for divorce 38 years ago after walking out on his wife to live with a mistress, was entitled to court consideration of his divorce suit even though he was the person at fault.

The businessman, who has two children with his mistress, had been denied a divorce by two lower courts after those courts refused to recognize his demand. The businessman and his 71-year-old wife, with whom he has not lived since 1949, were not identified in court papers.

The Supreme Court ruling is being hailed as the beginning of a new era in Japan, which has approved very few no-fault divorces in comparison with the United States and Europe.

Under Japanese civil law a person can sue for divorce only in cases of adultery, desertion, absence of the spouse for more than three years without contact, incurable mental illness or instances such as maltreatment that make continuation of the marriage impossible. Generally, Japanese courts have held the view that "guiltless" spouses should not be forced into unwanted divorces.

Japanese legal experts said today that the Supreme Court decision reflected changing social reality. Japanese marriages now more often result from love than official arrangements, and divorce has become acceptable.

"In a word, it is the new trend of the times," said the lawyer for the shunned wife, Hiromasa Kido.

Because of the stigma attached to divorce and the absence of laws guaranteeing child support, alimony and property division, Japanese wives -- most of whom stay at home with their children -- have long felt it better to suffer in silence than risk divorce, experts say.

According to court statistics, women get custody of the children in most divorces, but only in slightly more than half of court-mediated cases have men agreed to divide property and offer alimony.

Nonetheless, the number of divorces has more than doubled in the last two decades, and women are asking for the separations. But Japan's divorce rate is still well below that of other industrial countries. For instance, the United States had 5 divorces per 1,000 married people compared with 1.5 per 1,000 in Japan in 1983.

"It is not natural that a husband and wife who hate each other should live together. So from that point of view I agree with today's verdict," said Yoriko Madoka, head of an organization for amicable settlement of divorces. "But the reality of Japan today is that divorce is overwhelmingly disadvantageous for women . . . . It is necessary to have a law which requires men to assure the life of their ex-wife and children."

About 90 percent of Japan's divorces, unlike the case decided today by the Supreme Court, are uncontested. When husband and wife agree on the terms of divorce, a final parting of the ways can be obtained simply by filing a short document at the local government office.

However, today's case was more complicated. The husband and wife married in 1937 -- for love -- but when his wife discovered he was having an affair, the husband moved out in 1949 to live with his mistress, a widow with two children. The married couple had had no children together.

The wife got the couple's house and supported herself by selling it and becoming a teacher of doll-making. Today, according to newspaper reports, she has tuberculosis and lives with her older brother.