To provide a positive and negative pressure relaxation device for a drain facility system, which can smoothly drain water even if the drain facility system has a trap structures on an upstream side and a downstream side, by relaxing positive and negative pressures in a drain pipe between the traps, and imparts high functionality to the traps while maintaining the smooth draining performance, to thereby achieve the drain facility system of various modes.

The drain facility system 1 has the upstream-side trap 3 structure formed in a drain facility 2, and the downstream-side trap 9 structure located at an intermediate location of the drain pipe 8. The positive and negative pressure relaxation device for the drain facility system has a positive and negative pressure relaxation mechanism 11 for relaxing the positive and negative pressures in the drain pipe 8 in the upstream-side trap 3 structure.