Bicycle hub outer and bicycle hub

A rear hub 15 has a hub shaft 43 and a hub outer 61 that is configured to be mounted in a freely rotatable manner to the hub shaft 43. The hub outer 61 has an outer main body 71 and an adapter 73. The outer main body 71 is arranged on the radially inward side of a sprocket, and has a first rotation preventing section 71a that engages with an engaging section of the sprocket in such a manner that the outer main body 71 cannot rotate relative to the sprocket. The adapter 73 is mounted in a freely rotatable manner on an adapter mounting section 71b of the outer main body 71. The adapter includes a second rotation preventing section 73a that engages with the engaging section of the sprocket in such a manner that the adapter 73 cannot rotate relative to the sprocket.