To provide a waterproof sheet structure which allows maintenance work to be easily performed and prevents a waterproof sheet from being cracked or cut even when a screw head is lifted due to time degradation.

A waterproof sheet structure includes a disk 2 fastened to a surface of a floor material 1 with a screw 3, and a waterproof sheet 4 laid on the floor material 1 of which rear face 41 is bonded to or welded to a surface 21 of the disk 2. In order to prevent fixation of a head 31 of the screw 3 and the waterproof sheet 4, a fixation prevention sheet 5 is arranged between the head 31 of the screw 3 fastening the disk 2 and the rear face 41 of the waterproof sheet 4 which falls on the head 31.