The present invention relates to a float used as a buoyancy body on water when an ocean floating structure such as an aqua-farm is installed. More specifically, the present invention relates to a lightweight float which has excellent corrosion resistance against seawater, can prevent environmental pollution, can be reused when broken, is eco-friendly, can be filled with a predetermined kind of gas, such as helium, or water, has buoyancy capable of being increased and decreased depending on the kind of the ocean floating structure when needed, can minimize shaking, generated by waves, of the ocean floating structure in stalled on an upper side of the float, and thus can enable a user to more stably perform work on the ocean floating structure even when wave heights are high in bad weather conditions. According to the present invention, the lightweight float (1) is formed in a cylindrical shape having an empty space therein and comprises: circular grooves (10) in a certain depth which are formed on left and right circular side ends； gas injection units (11), formed in centers of the circular grooves (10) of the left and right circular end sides in one direction, and transfer protrusion units (12) formed on the inner circumferential sides of the circular grooves (10) of the circular end sides in other directions； joining grooves (20) formed on left and right outer circumferential sides in lateral sides in a lengthwise direction； and multiple fluid flow grooves (21) arranged at predetermined intervals on the outer circumferential sides of lateral sides in a lengthwise direction between the joining grooves (20).본 발명은 양식장 등의 해상 부유 구조물의 설치시 수상 부력체로 사용되는 부자에 관한 것으로, 좀 더 상세하게는, 해수에 대한 내부식성이 우수하여 환경오염을 방지할 수 있고, 파손시 재활용이 가능하여 친환경적이며, 부자 내에 헬륨 등의 소정 가스나 물 등을 주입할 수 있어 해상 부유 구조물의 종류에 따라 필요시 부력을 증감할 수 있고, 파도에 의한 부자 상측에 설치된 해상 부유 구조물의 흔들림을 최소화할 수 있어 나쁜 기상조건에서 파고가 높은 경우에도 보다 안정적으로 해상 부우 구조물 상에서 작업을 수행할 수 있도록 하는 경량 부자에 관한 것으로,본 발명에 따른 경량 부자(1)는, 내부에 빈 공간이 구비되는 원통형 형상으로 형성되며； 좌, 우
