To further surely prevent leakage of water of a reclaimed area to the outside through a revetment by further enhancing the impervious performance of the revetment surrounding the reclaimed area.

The impervious structure at the revetment of the reclaimed area seals water between an impermeable flexible membrane 9 laid on a slope 8 formed in a part 4a of the revetment 4 surrounding the reclaimed area 3 and downward tilted toward the bottom of the reclaimed area 3, and a revetment structure 14 constituting other parts 4b of the revetment 4 and continuously formed at a part 4a of the revetment 4. An impermeable plate 16 is mounted on an inner wall face 15 of the side facing the reclaimed area 3. An edge part 25 on the revetment structure 14 side at the impermeable flexible membrane 9 is connected to the impermeable plate 16 side by an adhesive 11.