An optical fiber not only can suppress SBS but also can be produced easily. The optical fiber 1 comprises an optical core region 10 including the center axis and an optical cladding region 14 surrounding the optical core region 10. The optical core region 10 is composed of a first region 11, a second region 12, and a third region 13 in this order from the inside. The third region 13, which is a part of the optical core region 10, is a ring-shaped acoustic core region. The propagation mode of an acoustic wave can be localized in the third region 13.