A buoy system according to one embodiment of the present invention includes a buoy body configured to provide buoyance; a fixing belt configured to fasten the buoy body to a ship structure; an auto-release unit configured to release the buoy body to be buoyed by releasing the fixing belt when a predetermined water pressure is reached; and an auto-reel chain box fixed to the ship structure, being opened in conjunction with releasing of the fixing belt, and including a chain which is reeled out when the buoy body is buoyed, wherein the auto-reel chain box comprises: a weight provided in the auto-reel chain box and being movable upward and downward according to a water pressure and buoyance; a pulley provided in the auto-reel chain box, having the chain wounded thereon and a plurality of teeth on an outer circumferential surface thereof; and a shaft having one end connected to the weight and the other end engaging with the teeth to fix the pulley and provided to be rotatable around a portion fixed in the auto-reel chain box.