It is referred to as 'Ryusaku no kan' ('龍作の官', post created by a dragon), due to the note 'Dragon, create a nagon!' in Shokyo (one of the five classic texts of Confucianism).
「龍作の官」と呼ばれるのは書経に「龍、なんじ納言（言をいれる）を作（な）せ」とあるのによる。