Tokyo - A bill allowing 83-year-old Emperor Akihito to abdicate cleared the more powerful chamber of Japan's parliament on Friday, setting the stage for his elder son to succeed the Chrysanthemum throne.The bill, approved unanimously by the lower house, now moves to the upper house for enactment expected next week. An abdication, which under the bill would need to take place within three years, would be Japan's first in 200 years.Akihito expressed his apparent wish to abdicate last summer, citing his age and health.That revived a debate about the country's 2 000-year-old monarchy, one of the world's oldest, as well as discussion about improving the status of female members of the shrinking royal population. The current male-only succession rules prohibit women from succeeding to the Chrysanthemum Throne and female members lose their royal status when they marry a commoner.Akihito was 56 years old when he ascended the throne in January 1989 after the death of his father, Emperor Hirohito. Crown Prince Naruhito, the first in line to succession, is 57, but his only child is a girl. His younger brother, Prince Akishino, has two adult daughters and a 10-year-old son.The government has avoided divisive issues such as whether female emperors should be allowed. But the royal family will be losing another member with the coming marriage of Princess Mako, one of Akihito's three granddaughters, triggering concerns about a shortage of heirs.The abdication bill is special legislation only for Akihito and expires in three years, a way to avoid putting future monarchs at risk of forcible abdication due to political manipulation. Media reports have said officials are considering Akihito's abdication at the end of 2018, when Akihito turns 85 and marks 30 years on the throne.The legislation for Akihito's case was needed because the 1947 Imperial House Law does not provide for abdication. The last emperor to abdicate was Kokaku in 1817.Ultra-conservatives in Prime Minister Shinzo Abe's ruling party have also reluctantly agreed to adopt a non-binding resolution calling for the government to study ways to improve the status of female members in the monarchy.