PROBLEM TO BE SOLVED: To provide a waterproofing device of an opening, capable of preventing an upper end of a waterproof sheet form coming off an opening/closing body.SOLUTION: A waterproofing device of an opening includes: a sheet 10 communicating an indoor side of a structure S with an outdoor side of the structure S, and installed in an opening O opened and closed by an opening/closing body 4; holding members 20 for holding the sheet 10 to the structure S at a position on an outdoor side with respect to the opening/closing body 4; and fitting members 30 for fitting an upper end 12 of the sheet 10 to the opening/closing body 4. Each of the fitting members 30 comprises: a sheet fitting part 30a attached to the upper end 12 of the sheet 10; an opening/closing body fitting part 30b attached to the opening/closing body 4; and a connection part 30c for connecting the sheet fitting part 30a to the opening/closing body fitting part 30b, and allowing a distance between the sheet fitting part 30a and the opening/cl
