A device for attaching a cross-member of a dashboard to a front pillar lining, the device including: a reinforcing element including a first positioning element for cooperating with a second positioning element secured to the dashboard such that they occupy a relative determined position. An attachment element is used to immobilize the assembly in the determined position. The attachment element is configured such that the connection between the first positioning element and the reinforcing element includes a position regulating mechanism configured to vary between an unlocked state in which the position of the first positioning element is adjustable in relation to the reinforcing element, and a locked state in which the first positioning element is fixed in relation to the reinforcing element.