The Kantei or 官邸 is the official residence of the Prime Minister of Japan: think of it as the Tokyo equivalent of the White House or 10 Downing Street. It is located in Nagata-cho, down and across the street from the Diet Building.

The first Kantei was a two-story mansion, heavily influenced by Frank Lloyd Wright, built in 1929 for Prime Minister Tanaka Giichi. Today, the old Kantei has a "mystery" bullet hole in its glass facade. Nobody is entirely sure how it got there: some believe that the bullet was fired during the February 26 Incident, while others attribute it an uprising in August of 1945, and still others say that it comes from a student revolt in 1960.

A new five-story Kantei was finished in April of 2002 at a cost of $350 million, and is now occupied by Junichiro Koizumi. The new Kantei is designed in a uniquely half-Japanese, half-Scandinavian, and somewhat-Star Trek architectural mode. Most of the walls are sectional and made of wood: the ceiling lighting is designed to resemble the paper walls of old Japanese houses. The middle of the building is occupied by a rock garden. To accommodate the growing needs of world leaders, the new building has two helipads on the roof as well.

One of the biggest complaints about the new Kantei is that the press have virtually no access to the prime minister now. At the old Kantei, they could just wait outside his office door and harrass him as he walked through the hallway. Now, the entire fifth floor, where Koizumi's offices are located, is shut off to the public, so the press have to wait outside the gate.