Abstract: A spring-compressor device comprises a body having at least two telescopic parts (1, 4, 7) fitted with respective coupling means (2, 9) for jaws (3, 10), and including means internal to the body for controlling lengthening or shortening thereof. The innermost part (7) of the body is constituted by the body of a single-acting actuator whose rod (11) which is secured to the piston (12) of the actuator is fixed to the outermost part (1) of the body and is provided with a duct (14) for feeding the chamber (13) of the actuator whose increase in volume tends to retract the body of the compressor.