To provide a rod tensioning device which is compact in a radial direction.

The rod tensioning device (2) includes an actuator (6) for generating tensioning axial force (F), a tie-rod (7) for conveying the axial force from the actuator (6) to a threaded section (1b) of the screw rod (1), and a locking element (42). The tie-rod (7) is radially movable between a closed position where the tie-rod (7) is engaged with the threaded section of the screw rod (1) and an open position where jaws (27) are disengaged from the threaded section (1b) of the screw rod (1). The locking element (42) has a sleeve (43) which is axially slidable in the vicinity of the jaw (27), and the sleeve (43) has a truncated-conical internal surface (45) coming in contact with the corresponding outer surfaces of the jaws (27).