To provide a piping structure, preventing entering of dust into the device side.

This piping unit 1 is formed of an inflow port 2 opened downward, an outflow port 3 opened upward, and a drain port 4 opened sideways. A drain plug 5 having a filter 6 is screwed in the drain port 4, and the drain port 4 can be opened by removing the drain plug 5. In an outflow port 3 downstream from the filter 6, a second filter 7 composed of a fitting ring 8 and a wire net 9 swollen downward with the peripheral edge thereof fixed to the fitting ring 8, whereby even if the drain plug 5 is detached with the filter 6, entering of dust to the downstream side through the outflow port 3 can be inhibited by the second filter 7.