Governmental systems and administrative organizations in Iran have been always in change throughout history. A position which was necessary in some centuries and was counted as an important governmental position was “Amirdadi”. The person who held this post was called Amir-e dad or Mirdad. Lexicographers have mentioned several different tasks for Amir-e dad. Some believe they are the same as chief judges. Some have considered them as the executers of the King’s commands in Mazalem (justice) days. And some others have assumed they are the administrators who were responsible for public affairs. Some also have mentioned them as ministers or administrators of the Ministry of Justice. In this article the researcher attempts to answer this essential question: What position did Amir-e dad have in old administrative organization and for which tasks he was responsible? This article consists of four sections: in section one, the word structure of Amir-e dad is studied. Section two analyzes the era in which this term was prevalent. Section three describes the tasks and positions of Amir-e dad in governmental systems in which this post had been officially recognized, on the basis of some available literary and historical evidences. Finally, in section four, some points are mentioned on the ceremony of Amirdadi empowering.