To prevent duplication of a plug in pneumatic transportation piping.

A bend part 5 ha an inner tube 51, an outer tube 52, an inside passage 10, and an outside passage 11. A ferrule (or such as a flange) 53 is formed in an upper end part, and a ferrule 54 is formed in a lower end part, respectively integrally. An air communicating passage (a hole) 55 is penetratingly arranged. For example, a metallic (for example, sintered metal) ventilating filter 57 is arranged in a bottom surface part of a bend. The position is desirable in the bottom surface part, and is allowable in a proper position. Since the inside of the outside passage 11 is filled with high pressure auxiliary air, the high pressure auxiliary air is supplied to the inside passage 10 from the outside passage 11 via the filter 57 to fluidized the plug as well as to prevent a pressure drop inside of the inner tube 51.