An adjustable bar-guiding device includes at least one pair of complementarily-shaped jaws which are slideably associated with a fixed frame with the interposition of at least one movement lever mechanism which is actuated by at least one fluid cylinder. The jaws perform a translational motion according to a stroke of mutual approach/spacing apart, between a first configuration of substantial juxtaposition of their respective surfaces and a second configuration in which the surfaces are located at a predefined distance for containing a bar.