The invention concerns a rod tensioning device having a first actuator, at least a second actuator and a tubular support sleeve dedicated to radially surround a threaded rod. Each of the actuators provides a cylinder, and a piston sliding in the cylinder and forming with the cylinder an annular chamber dedicated to be supplied with pressurized fluid. According to the invention, the at least second actuator is temporary axially arranged between the first actuator and the tubular support sleeve for a temporary blockwise assembly, the pistons of two axially adjacent actuators being indexed in rotation together.