PURPOSE: To prevent a toilet bowl leg part from being broken or cracked by an excessive fastening by arranging a gasket consisting of two vertical layers consisting of unvulcanized butyl rubber and vulcanized rubber between a drainage flange and the outflow hole of the waste passage of a toilet bowl, and connecting the unvulcanized butyl rubber to the outflow hole side of the waste passage of the toilet bowl.

CONSTITUTION: An annular gasket 17 to be arranged between a drainage flange 3 and a toilet bowl 7 is formed of a vertical two-layer structure consisting of an unvulcanized butyl rubber 15 and a vulcanized rubber 16. The gasket is set on the drainage flange 3 in the state where the vulcanized rubber 16 is placed on the annular recessed part 3b of the drainage flange 3 mounted on a floor 1 to situate the unvulcanized butyl rubber 15 upside. The outflow hole 9 of the waste passage 8 of the toilet bowl 7 is situated above a soil-pipe 2, and the toilet bowl 7 is fastened by the T-bolt 10 and nut 12 installed to the drainage flange 3. Further, a hollow part 19 is formed in the vulcanized rubber 16. Thus, the air in the hollow part 19 is discharged to the outside through a small hole 18 even with a small fastening torque, and the hollow part 19 can be thus deformed to ensure a sufficient fastening margin.