Josu entered the Buddhist priesthood under Eshuku of Jogan-ji Temple at a very young age and went on to be consecrated by Shobo of Daigo-ji Temple in the year 902.
幼くして貞観寺恵宿の室に入り、902年（延喜2年）醍醐寺聖宝から伝法灌頂をうけた。