To provide a working waterproof sheet which forms a box space covering an opening part outside the opening part of a building or the like.

The working waterproof sheet comprises a sheet main body 10 covering the opening portion b and a portal frame body 20 arranged inside the sheet main body 10. The sheet main body 10 comprises an upper surface part 11, surface parts 12, 13 on both sides and a front surface part 14. An upper peripheral part locking means 15, which locks the upper surface part 11 to the locking part f1 arranged to a building B, is provided to the end periphery corresponding to the opening part b of the upper part 11. A fixing means 18, which fixes the upper side part 21 of the portal frame body 20, is arranged to the inner surface boundary part between the upper surface part 11 and the front surface part 14. A pocket 19, into which the lower end part of the portal frame body 20 is inserted, is provided to a lower end on the opening side of both side surface parts 12, 13. The portal frame body 20 is retained with a fixing means 18 and the pocket 19 within the sheet main body 10. Thereby, the side parts 22, 23 on both sides of the portal frame body 20 retain the sheet main body 10 while making the sheet main body tight, inclined with respect to a vertical line.