Daijokan was established as an organization integrating the roles of two ministries in the Tang government, Monkasho, responsible for deliberation of imperial documents, and Shoshosho, responsible for administration, with two ministries of Shonagonkyoku, that functioned as Monkasho, and Benkankyoku, that functioned as Shoshosho; however, Giseikan functioned as a deliberation branch, the essential power of Shonagonkyoku was lost, while Benkankyoku, responsible for civil service, gained power to exert its influence on Geki, the office placed under Shonagonkyoku.
太政官は唐の制度における門下省（審議）と尚書省（行政）の役割を統合した性格を有しており、門下省的な役割を担った少納言局と尚書省的な役割を担った弁官局が並立したが、議政官が実際の審議機関となったことによって少納言局の権限が形骸化される一方で、行政事務を管轄する弁官局の力が強まって、外記に対しても影響を行使するようになったとされている。