THE STUDY ON OUTFLOW OF JUNIOR HIGH SCHOOL STUDENTS FROM THEIR HOMELAND IN ISOLATED ISLAND IN JAPAN-THE CASE OF TSUSHIMA CITY, NAGASAKI PREFECTURE- 2018年5月21日 THE STUDY ON OUTFLOW OF JUNIOR HIGH SCHOOL STUDENTS FROM THEIR HOMELAND IN ISOLATED ISLAND IN JAPAN-THE CASE OF TSUSHIMA CITY, NAGASAKI PREFECTURE-