To provide a plastic cylindrical body which is easily floats on water and is substitutable for bamboo floating on a sea surface for cultivating marine products by forming a joined cylindrical body by joining the plural pieces of the cylindrical bodies made of plastic on both sides of one or plural pieces of joint node bodies and forming a space part sectioned by the joint node bodies inside the joined cylindrical body.

For instance, the joined cylindrical boy is formed by joining the cylindrical body 2 made of the plastic to the joint node body 1 and the space part 4 sectioned by the joint node body 1 is formed inside the joined cylindrical body. The space part 4 is turned to an air-tight state hidden by the joint node body 1 and the cylindrical body 2. The joint node body 1 is provided with a flange part 10 to be projected in a node flange shape from the outer peripheral of the joined cylindrical body at the time of forming the joined cylindrical body and joint parts 11 and 12 joined with the wall part of the cylindrical body 2 in a tightly adhered state. Also, the joint node body 1 and the cylindrical body 2 are molded by a molding resin material mixed with a foamed material, the joined cylindrical body is reduced in weight and this cylindrical body is obtained.