Device (1) for tensioning parallel threaded rods, comprising a plurality of actuators (4, 5) able to exert a tensile axial force, each actuator (4, 5) being associated with a tie rod (19) that transmits the tensile axial force to one end of one of the threaded rods, a lower crown (3) and an upper crown (2) which are coaxial, a plurality of lower hydraulic chambers being formed in the lower crown (3) and a plurality of upper hydraulic chambers being formed in the upper crown (2), an annular actuator piston (14) being positioned in each hydraulic chamber (15), the distance between the axes of two adjacent pistons (14), one positioned in a lower hydraulic chamber and the other positioned in an upper hydraulic chamber being smaller than the diameter of said pistons (14).