Sangdaedŭng (Korean: 상대등; Hanja: 上大等, the First of Taedŭngs or Peers, Extraordinary Rank One) or Sangsin (상신; 上臣), was an office of the Silla state.
He presided over the Hwabaek Council (화백; 和白), an advisory and decision-making committee composed of other high-ranking officials holding the office of Taedŭng (대등; 大等).
During the middle period of Silla, following that state's unification of the peninsula, the focus of government authority shifted from the Hwabaek Council and Sangdaedŭng to the Chancellery Office (Jipsabu, 집사부; 執事部) and its Chief Minister (Sijung, 시중; 侍中, or alternately Jungsi, 중시; 中侍), an office instituted in Silla in 651 as the highest organ in the central government apparatus.
This reflected the monarchy's efforts to curb the power of an independent nobility by relying on the Chinese inspired Jipsabu rather than the Hwabaek Council, whose existence was predicated on age old aristocratic and clan prerogatives.
In the wake of several challenges to his authority King Sinmun dared even execute the Sangdaedŭng Gungwan in 681 for complicity in the revolt of Kim Hŭmdol (김흠돌; 金欽突).