Abstract: The present invention relates to a moving device for intervening inside small-diameter pipework. The technical field of the invention lies in constructing measurement apparatus for monitoring pipework and capable of moving along the inside of the pipework in substantially independent manner driven by thrust from the substance conveyed by the pipework acting on the device. According to the present invention, the device comprises a drive piston itself made up of at least two flexible and strong annular tractor cups and defining a sealed section of inside surface, and at least one third centering cup disposed between said two tractor cups. The supports for said cups are interconnected axially in pairs by respective traction cables associated with respective springs surrounding said cables, each spring bearing at each end against said supports of two consecutive cups, and serving to keep said cable under tension.