Abstract: The disclosed device comprises two support end assemblies formed as cup-shaped sleeves adapted to be alternatingly engaged with the internal surface of a pipeline and interconnected by a motion member. The lateral surface of each sleeve defines and annular chamber with an elastic sheath thereby. The two sleeves are interconnected by a bellows fixed between the bottoms of the sleeves. The annular chambers and the bellows are connected to an air-compressor through an automatic control system arranged so that at the initial stage of a successive advancing step the leading chamber communicates with the ambient atmosphere, while the trailing chamber and the bellows are communicated to the pressure connection of the compressor, whereas at the final stage of the step the trailing chamber and the bellows are communicated with the suction connection of the compressor, while the leading chamber is under pressure.