Headrest for an automobile seat

The headrest (1) has an angular adjustment device (4) for adjusting support structures (2, 3) relative to each other. The device includes detent protrusions (11a, 11b) exiting from one the structures. The protrusions are placed at sides of diameter of a circle to engage diametrically opposite notches (10a, 10b) of a clamp in tightened configuration. A passage from an angular position to another angular position makes deformation of the clamp toward its loosened configuration against elastic return force for returning the clamp toward the tightened configuration.