To provide a constantly clean sanitary environment by making drainage smooth and rapid by positively generating a swirl flow in a drain pipe when draining after the use of a sink, a bathtub, or the like, and naturally eliminating water scale or the like stuck into the drain pipe by the swirl flow operation of drainage.

The hole edge parts of water flow holes a, a, a in a perforated plate 3 fittingly mounted to the lower inside of a drain port 1 are formed as obliquely inclined edges b, b, b, or obliquely inclined water flow guide pieces are integrally added to one-side hole edges to positively generate the swirl flow to a water flow falling into the drain pipe 4 from the water flow holes a, a, a.