A device for pulling open continuously cross-conveyed tube sections for the purpose of forming bottoms in the manufacture of sacks has support tubes provided in pairs and connected to vacuum sources by lines. Each of the support tubes forms the coupler of two parallel connecting rods housed in a machine frame so as to rotate and is equipped with a row of radial suction units. A crank is connected to a shaft of a parallel connecting rod. A crank pin, supporting a slide ring or a roll, slides in a radial guide attached to a shaft. The shaft of the guide is offset relative to the parallel connecting rod shaft such that an essentially translational movement corresponding to the conveyance speed is superimposed on the opening movement of the row of suction units. In order to achieve a better opening of the tube section ends even at higher conveyance speeds, the radial guide is formed in a curved shape such that the time of uniform motion of the suction units and the tube section is lengthened.