Shibichudai was a household agency of the Empress Komyo (at the time when Shibichudai was established, she was already Empress Dowager Komyo since her husband the Emperor Shomu had abdicated the throne to his daughter the Empress Koken) which was established by FUJIWARA no Nakamaro (also referred as EMI no Oshikatsu) in 749. It was a Ryoge no kan (an organization outside of the Ritsuryo code).
The agency originally called Kogogushiki (the empress household agency) or Kotaogogushiki (the empress dowager household agency) was renamed according to the Tang-style name of Shibichudai. Though it was a household agency, it held the authority to implement the order (ryoji (orders issued by princes, empresses and so on)) of the Empress Dowager Komyo as well as exercise military power. It became the de facto supreme authority and military arm of the nation according to Nakamaro's expansion of power. Its status was equivalent to Daijokan (council of state) and its head called Shibirei was treated equal to that of Dainagon (chief councilor of state). When Shibirei was renamed Shibinaisho and came to be treated equal to that of the minister on June 15, 757, it seized the full power of Daijokan's ministers and obtained the authority to implement the Emperor's order without consulting Daijokan and Chumusho (Ministry of Central Affairs). It is believed that Shibinaisho played an equivalent role to that of Uchitsuomi (a important governmental post presiding over important state affairs while assisting the Emperor). Although it was ostensibly a household agency of the Empress Dowager Komyo, it was actually a military and administrative organization of the Empress Koken and FUJIWARA no Nakamaro faction that was established in order to cope with the anti-Nakamaro and anti-Koken movement which was then active involving Daijokan (the revolt of TACHIBANA no Naramaro occurred two months later).
When Tang-style names were adopted for government organizations in 758, it was renamed Kongukan and defined as the organization to 'receive the Imperial orders and convey them to government officials.'
As a result, Shibinaisho was put into a position to convey and implement the order of the Retired Emperor Koken and the Emperor Junnin in place of Daijokan and became the organization comparable to Daijokan both in name and reality. Nakamaro served as its head from the very beginning, but the post of Shibinaisho became vacant when Nakamaro was appointed to Oho (Udaijin (Minister of the Right) and became the top of the Daijokan in 758. Since then, its significance faded gradually though it was still under Nakamaro's charge, and was abolished when the Empress Dowager Komyo died in 760. However, according to Shoso-in Monjo (Shoso-in Archives), Kongukan (Shibichudai) was involved in a sutra-copying project conducted on the first anniversary of the Empress Dowager's death. Further, a description concerning the replacement of runaway shicho (servant) of Kongukan is found in the official document dated January 26, 762 that was written by Governor of Kai Province after the first anniversary of the Empress Dowager's death (official documents) (appears in the volume four of "Dai Nihon Komonjo" (Old Documents of Japan)). Judging from the above facts, it is believed that it was actually abolished around 762.
Though its significance had already faded, the abolition of Shibichudai was not only a big blow to Nakamaro but also a remote cause of the collapse of Nakamaro administration since it was independent from Daijokan and held its own military power as well as the authority to convey Imperial orders. After having overthrown Nakamaro, the Empress Shotoku (formerly, the Empress Koken) established Nijusho (Ministry of Royal Pages), a military organization modeled after Shibichudai, as a permanent Ryoge no kan.
Shibirei (director general of Shibichudai) (corresponds to Shosanmi (Senior Third Grade)): renamed Shibinaisho (from 757).
Daitsu (Senior assistant president), Shotsu (Junior Assistant president)
Daichu (Senior inspector), Shochu (Junior inspector)
Daiso (Senior officer), Shoso (Junior officer)
Shibu (low rank officials)