To solve the problem that, since a place where foreign substances are stagnated is located outside of a strainer element, when removing a strainer cap in order to remove and clean up the foreign substances, the foreign substances may be easily scattered around and further, when a device including a drain trap is located indoors, the ambient situations should be taken into account, so that it is necessary to carefully perform cleaning for wiping away the foreign substances, especially.

Compressed air and drain water which is generated by cooling and making into dew the compressed air using a refrigeration type air dryer 10 are fed into an element which constitutes a drain separator 30 and separates gas/liquid and foreign substances, as a fluid mixing both. The fluid is formed to pass through the element all and to stagnate the foreign substances internally and while the drain water is stagnated inside the bottom of the drain separator 30, the bottom of the drain separator 30 is connected to an electromagnetic drain trap 50, thereby discharging the drain water with power of the compressed air.