There is disclosed an adapter ring for rotation of a photographing lens barrel, the adapter ring being fitted into an outer periphery of the photographing lens barrel, the adapter ring being rotated through engaging with a ratchet wheel having a plurality of pawls which ratchet wheel rotates in conjunction with a dial disposed in a waterproof protector. This adapter ring has: a plurality of first projecting portions arranged in a predetermined angle range around an optical axis in the outer periphery to engage with the pawls of the ratchet wheel; and a plurality of second projecting portions which are the same plurality of projecting portions as the plurality of first projecting portions, the second projecting portions being arranged in a predetermined angle range but out of the predetermined angle range of the plurality of the first projecting portions.