DRAINING DEVICE

PROBLEM TO BE SOLVED: To prevent the backflow of water by retaining, in the position where water vertically flows and a downstream drain pipe diameter is extended relative to an upstream drain pipe diameter, an independent member having a diameter larger than the upstream drain pipe inside diameter and floating on water within the downstream drain pipe. SOLUTION: A drain pipe 1 comprises an upstream part 2 and a downstream part 3, with the inside diameter of the downstream part 3 set larger than the inside diameter of the upstream part 2, and an independent member 4 and a support member 5 are provided within the downstream pipe. In the state where the independent member 4 is situated in the bottom part of the support member 5, the total passage area 6 not blocked by the independent member 4 is set larger than the inside diameter of the upstream part 2. Since the independent member 5 has the characteristic of floating on water to block an upstream drain port 7, the backflow of water from the downstream part 3 to the upstream part 2 can be prevented. Accordingly, the leak of the drain pipe internal odor or the overflow of sewage can be prevented.