It is said that he was from a family of the Shimazu clan descended from the Koremune clan, and was a younger (or elder) brother of Tadahisa SHIMAZU, who held the title of Satsuma shugoshiki (provincial constables of Satsuma Province).
惟宗氏の流れを汲む島津氏の一門で、薩摩国守護職島津忠久の弟（あるいは兄）と伝える。