Abstract: A pneumatic device for fitting cables in a tube with improved unit safety in the event of excess pressure, comprises a capsule adapted to be introduced inside a tube and connected to a line used to pull the cable inside the tube. A unit (9) has a connection (20) to a compressed air source and a compressed air outlet connector (18) adapted to be connected in a substantially sealing-tight relationship to one of the ends of the tube. The unit comprises a distributor (19, 23) for distributing compressed air to the outlet connector (18), this distributor co-operating with discharge structure (32, 28, 29) to discharge the compressed air from the unit (9) in the event of an excess pressure downstream of the unit outlet connector (18).