Dai-ichi Seimei Hall, High-rise building in Yurakucho, Tokyo, Japan.

Dai-ichi Seimei Hall was a building completed in 1938 facing the Hibiya moat in Yūrakuchō. Its west side had ten square columns, and the facade was steel-framed stone with a wall-and-window rhythm. The east portion was demolished in 1989; the west portion was renovated and kept as the main building of DN Tower 21 in 1995.

Dai-ichi Seimei Hall was completed on 3 November 1938 on the former site of the Metropolitan Police headquarters, after a design competition drew 268 entries. During the Pacific War the Eastern Army District Command was stationed there and anti-aircraft guns stood on the roof. From 1945 to 1952 it housed the General Headquarters of the Allied Powers. The east wing was demolished in 1989; the west wing was renovated and reopened in 1995 as the main building of DN Tower 21.

The name Dai-ichi Seimei Hall refers to the headquarters of Dai-ichi Life Insurance, completed in 1938. From 1939 the company ran the private Hibiya Girls' School inside it, with president Taizō Ishizaka as headmaster; lessons ran from 5:30 to 8:30 pm for employees who had joined straight after primary school. The MacArthur Memorial Room on the sixth floor, kept from the occupation years, is open to visitors.

The location is just a minute's walk from Yūrakuchō Station and connects directly to Hibiya Station through underground passages. This central position makes it easy to reach whether you arrive by train or explore the surrounding neighborhood on foot.

Inside the building is a memorial room that preserves the original office space where major decisions about Japan's recovery were made during the occupation years. This preserved interior offers visitors a direct look into where post-war administration actually happened.