Initially, a specific court noble privately designated by the bakufu assumed the post, but after Michiie KUJO lost his position in 1246, it became an official post designated by the bakufu and the post was hereditarily assumed effectevely by the head of the Saionji family that had a marital relation with MINAMOTO no Yoritomo (his niece entered the Saionji family through a marriage).
初めは幕府側の私的な指名を受けて特定の貴族が就任していたが、九条道家が失脚した寛元4年（1246年）以後は幕府による指名によって任命される正式な役職となり、源頼朝と婚姻関係（姪の嫁ぎ先）があった西園寺家当主による事実上の世襲となる。