There is a theory stating that he was born in Tsushima Province, but it is now clear that he was born in Yamato Province (recently there has also been another theory that 'Sakon SHIMA' was a name of the Shima clan who served the Tsutsui clan and that there was another person named 'Sakon SHIMA' before Kiyooki).
対馬国出身説もあるが現在では大和国出身であることが明らかとなっている（近年では「島左近」は筒井氏家臣である島氏代々の名乗りで清興以前にも「島左近」を名乗る者がいたという説もある）。