PURPOSE: To simplify a piping system, make laying operation easy and lower the cost by integrating a separator, a strainer and a trap.

CONSTITUTION: A separator 4 wherein a strainer 10 and a trap 15 are integrated is installed in a steam piping system. Then, drain and impurities are separated from the stream by the separator 4 and the strainer 10, and drain is discharged out of the trap 15. As a result, by separating drain and impurities from steam in a steam piping, generation of water hammer or corrosion of piping are prevented from being general, and also a piping system and relative laying operation are simplified to lower the cost of manufacturing the separator, strainer and trap.