The Diet Building was completed in 1936 and is constructed entirely of Japanese materials, with the exception of the stained glass, door locks, and pneumatic tube system.

The Diet met in temporary structures for the first fifty years of its existence because there was no agreement over what form its building should take.

Böckmann's initial plan was a masonry structure with a dome and flanking wings, similar to other legislatures of the era, which would form the core of a large "government ring" south of the Imperial Palace.

In 1898, Prime Minister Itō Hirobumi interviewed American Ralph Adams Cram, who proposed a more "Oriental" design for the building, featuring tiled roofs and a large enclosure of walls and gates.

With an internal deadline approaching, the government enlisted Ende and Böckmann associate Adolph Stegmueller and Japanese architect Yoshii Shigenori to design a temporary structure.

Prime Minister Katsura Tarō (桂 太郎) chaired the commission, which recommended that the new building emulate an Italian Renaissance architectural style.

[2] The roof and tower of the building might have been inspired by another entrant, third prize winner Takeuchi Shinshichi, and are believed to have been chosen because they reflected a more modern hybrid architecture than the purely European and East Asian designs proposed by other architects.

While the actual source for the “Pyramid” roof remains unclear, Japanese historian Jonathan Reynolds suggests it was “probably borrowed” from Takeuchi although an image of the entry is not provided but instead he thanks fellow historian of Africa studies at Columbia, Zoe Strother, for mentioning that Takeuchi’s design resembles the Mausoleum at Halicarnassus,[3] which was a model for some prominent Western designs in the early 20th century, such as John Russell Pope's 1911 award-winning House of the Temple in Washington, D.C., and the downtown Los Angeles City Hall, completed in 1928.

The central entrance is not for daily use to enter and exit the Diet building and is called “the door that never opens” because of its restricted access.

The paintings each depict Mount Yoshino in the spring, Lake Towada in the summer, Okunikko in the fall, and the Japan Alps in the winter.

In the four corners of the central hall are statues of Itagaki Taisuke, Okuma Shigenobu, and Ito Hirobumi who were instrumental in establishing constitutional government in Japan, and an empty pedestal.

Others say designers left it open to urge politicians today to outstrip the three grand predecessors, or that they avoided erecting a statue with its back to the Imperial palace.

Inside the pyramid-shaped dome is a large hall, from the center of which a spiral staircase leads up to the observatory on the top floor of the tower.

Employees of Kajima Corporation who happened to be present at the scene to fix a restroom requested help from their own company which ended up being in charge of the repair work of the tower.

[4] The Gokyūsho (御休所) was originally referred to as Gobinden (御便殿) and was built as a place for the Emperor to rest upon his visit to the Diet to attend events like the opening and closing ceremonies.

In the House of Councillors, the Emperor's throne is at the top of the stairs behind the chairman's seat which will be removed in preparation for the opening ceremony.

No exceptions are allowed to this rule; then-Prime Minister Takeo Fukuda once attempted to enter the Chamber while forgetting to wear his badge and was halted by the guards, the situation of which was resolved when Fukuda hastily borrowed a member badge from a nearby Diet member, Yoshiro Mori.

Parenthetically, either House restricts its members from wearing hats, coats, scarfs, or carrying umbrellas or walking sticks without permission from the chairman.

The general public seats are partly assigned to guests invited by a Diet member with the rest open to visitors on a first-come-first-served basis.