The Supreme Court on Friday upheld lower court rulings in which advertising giant Dentsu Inc. was held responsible for neglecting to act to prevent the 1991 suicide of a 24-year-old employee who showed signs of depression from overwork.

The case, initially a civil court action filed by the parents of Ichiro Oshima, is the first in which the Supreme Court has ruled that a company has a legal responsibility for an employee's suicide caused by depression from overwork.

The top court also ruled that the advertising agency was more responsible for the death than the high court deemed in its previous ruling, and returned the case to the high court to decide on an amount of compensation greater than it had initially rewarded.

Both sides have appealed to the top court since the Tokyo High Court ruling in 1997, in which the court reduced the amount of compensation for Oshima.

While the high court acknowledged the relationship between depression from overwork and the subsequent suicide as well as the responsibility of the ad agency for failing to reduce Oshima's excessive overtime, it added that Oshima and his parents also had some responsibility for taking care of his health.

The presiding judge, Shinichi Kawai, and three other Supreme Court judges ruled Friday that employers have a duty to prevent their employees from suffering stress or mental fatigue from their work, and that Dentsu neglected to fulfill its responsibility over Oshima's excessive amount of work and overtime.

The top court also reversed the Tokyo High Court's ruling that Oshima and his family also were at fault, adding that Oshima, who was diligent and had a keen sense of responsibility, was not to be blamed for his character.

Dentsu had said Oshima volunteered for extra work because of his character.

After the Supreme Court ruling, Hiroshi Kawahito, the lawyer for Ichiro Oshima's parents -- Hisamitsu, 71, and Yoko, 64 -- said they were pleased that the top court effectively supported their claim.

"This is a remarkable Supreme Court decision and will be a landmark in the history of Japanese court trials," Kawahito said.

Kawahito added that Friday's top court's decision, which clearly admitted the relation between overwork and suicide as well as companies' responsibility for employees' safety, will influence similar ongoing trials and encourage people who have suffered similar losses.

"I am grateful to the judges of the Supreme Court for the decision," Hisamitsu Oshima said. "I believe that this will lead corporate management to improve the work environment."

Meanwhile, Dentsu officials said they will humbly accept the top court's decision and will act to improve work environment for its workers. They added a word of condolence about Oshima's death.

The legal proceedings began in 1993 when Hisamitsu Oshima, filed a suit against Dentsu demanding compensation for his son's suicide.

According to Friday's ruling, Oshima, who joined Dentsu in April 1990, had worked past 2 a.m. about four times a month in 1990. He was involved in the planning of commercials and events for the firm's radio promotion section and had 40 clients.

The frequency of his late nights at work increased to between five and 10 times a month in 1991; by August of that year he was working overtime two out of every five days. Most of the time he was unable to leave work before 6 a.m. the following morning, according to the ruling.

When Oshima returned home after these shifts, he basically only had time to change his clothes before returning to the office.

Around July 1991, Oshima reportedly told a superior: "I can't really sleep, and I wake up only after two hours of sleep," and "I don't know if I am useful as a human being."

Oshima hanged himself in the bathroom of his home in the Tokyo suburb of Machida on Aug. 27, 1991, after completing work on a major event for the listeners of a radio program that he was responsible for.

The Tokyo District Court ruled in March 1996 that Oshima's suicide was caused by depression due to exhaustion after working extraordinarily long hours.

The district court also ruled that Dentsu was at fault because it did not take any concrete measures to correct the situation, despite being aware that Oshima's health was deteriorating and his remarks and actions could have been regarded as signs of an impending suicide attempt.

Dentsu appealed the district court's ruling, claiming that according to records of working hours that Oshima submitted, he had only worked two or three overtime hours each day.

The advertising firm claimed that some of the tasks that workers perform when they stay late cannot be described as work, and that Oshima killed himself because of his family environment and personal problems.

In 1997, the Tokyo High Court handed down a ruling that basically followed the decision of the lower court but reduced the 120 million yen in compensation that the district court awarded to Oshima's parents to 89 million yen.

The high court said the amount was reduced because Oshima and his parents bore some responsibility for his excessive overtime hours and his health.

It ruled that Oshima had some say in how long he had to work and that his parents, who were living with their son at the time, did not take any measures to correct the situation. It also said Oshima could have taken steps to help himself, such as going to a hospital.

Both Dentsu and Oshima's parents appealed to the Supreme Court. Oshima's father said he does not agree that he and his wife were partly responsible for their son's suicide.

The Labor Standards Inspection Office recognized Oshima's death as a work-related accident in August 1998.