At its postwar inception, the National Diet Library was housed in the former Akasaka Detached Palace (now the Guest Palace). Phase 1 of the present NDL Main Building was completed in 1961 and Phase 2 in 1968. To keep up with the constant increase in materials and services, the Annex building was constructed and opened in 1986 except for some stacks. The entire Annex was completed in 1993. The total floor area of these two buildings is 148,000 square meters of which 53% is for stack space. Their stack capacity is about 12 million volumes. As a new facility, the Kansai-kan completed and the former Ueno Branch Library in Tokyo was transformed into the International Library of Children's Literature.

The Main Building

The Main Building of the National Diet Library has a centralized stack system. The stack space unit is 45m by 45m and has 17 vertical levels. The total stack capacity is 4.5 million volumes, with the widths of the stacks adding up to 172 km. For the preservation of library materials, the air conditioning keeps the temperature inside the stack space at about 22 degrees C and humidity at about 55%, and the fire extinguishing system employs carbon dioxide gas instead of water. For rapid movement of materials, the stack space is equipped with pneumatic carrier pipe and vertical/horizontal conveyor systems. The square administrative space unit surrounds the square stack space unit. Measuring 90m by 90m and rising six floors high, this unit contains a catalog hall, reading rooms for general visitors, reading rooms and research rooms for Diet Members, and library administration offices. The total floor area of the stack space unit and administrative space unit is 74,900 square meters.

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Well and hall

The Annex, located directly north of the Main Building, in a rectangular floor shape measuring 135m by 43m, with special design emphasis on natural and harmonious linkage with the Main Building, houses chiefly serials.
The building has four floors above ground and eight floors underground with a total floor area of 72,900 square meters. The stacks are entirely underground from the first basement to the eighth basement with a 7.5 million volume capacity with 2450 km of shelves. As a light well is provided at the center of the Annex, natural light can reach even the deepest underground floor. A vertical/horizontal conveyor system ensures rapid delivery and return of the stocked materials.

Annex stack room

Of the part above ground, the eastern half of the building is allocated to public space and the western half to offices. The reading space is around an atrium with skylights on the fourth level so that visitors can spot the locations of each reading room at a glance. The Annex also houses an exhibition room and an auditorium at its southeastern end.

The Kansai-kan of the NDL is a facility in the Kansai Science City with a large storage space for ever-increasing library materials and electronic library functions. The new facility operates in tandem with the present facility in Tokyo as a center of the NDL's document and information supply service.
The new building, designed by the winner of the international competition held in 1996, comprise four floors above ground and four floors underground with a total floor area of 59,300 square meters with a 6 million volume capacity. The abundant greenery and transparency of the glass exterior blend well with the surroundings. In the future, the building will be expanded in stages to a final floor space of 165,000 square meters with a 20 million volume capacity.
The building was completed in March 2002 and the Kansai-kan was opened to the public in October 2002.

The International Library of Children's Literature (ILCL) was partially opened to the public in May 2000 as a branch library of the NDL in the former Ueno Branch Library building. It was fully opened on May 5, 2002.
The Library building is being remodeled in two phases. Renovating the early twentieth-century building in order to house the ILCL, the NDL has sought to preserve the design and structure that is the legacy of earlier eras, while refurbishing the building using earthquake-resistant methods to minimize damage in a major tremor. The lot area is 6,300 square meters, the total floor space is 6,700 square meters, and the total stack capacity is 400 thousand volumes. The first floor is allocated to office area, Story Hour Room, Children's Library, and Meet the World. There are two Researchers' Resources rooms on the second floor, and the Museum on the third floor.