The prime minister's newly renovated residential quarters in Chiyoda Ward, Tokyo, opened Monday.
Former prime ministers, former chief Cabinet secretaries and other government ministers attended a luncheon to mark the occasion.
The four-story residential quarters are based on the former prime minister's office building, which was built in 1929.
The quarters stand next to the Prime Minister's Official Residence, which is an office complex for the prime minister and aides.
The building "has both historically and culturally high values, which have been preserved in new construction that is suitable for a new age," Prime Minister Junichiro Koizumi said at the ceremony in the renovated main hall.
Much of its interior has been renovated, including chandeliers, wallpaper, carpets and furniture. The former building was often described as being too old, small and gloomy.
The renovated house also has a room for conducting the traditional tea ceremony, as well as a Japanese-style room for entertaining foreign leaders.
