A floating body comprising a first swelling portion having a gas inlet port through which gas is introduced and a plurality of second swelling portions each being held in fluid communication with the first swelling portion. The first and second swelling portions are formed by folding a single multi-layer film to form a nonpleat portion corresponding to the first swelling portion and pleat portions corresponding to the second swelling portions and by sealing the folded multi-layer film along a continuous seal line which extends over both the pleat and nonpleat portions and forms the gas inlet port in the nonpleat portion.