To avoid breakage of a curtain by fixing one side end of a pollution preventive curtain unit to a mooring buoy and connecting the other side end to the following buoy with an easily detachable connection member to release the curtain unit in a storm.

Curtains 9, 9. are integrally fitted to floats constituted of floating bodies 12, 12 and tensile members 13, 13 to constitute a pollution preventive curtain units 21, 21. One side end of the unit 21 is connected to a mooring buoy 22 through a connection member 23 and the other side end is connected to the following buoy 22 by an easily detachable connection member 24. In this way, the units 21 are continuously connected to spread the curtains in site one after another. The units are disconnected by releasing the connection member 24 in a storm to keep the unit 21 free like a streamer while holding it only at one side end. Hence, the unit 21 can be prevented from being damaged.