Headrest for an automobile seat

The head-rest has an adjusting device arranged such that a moving part (3) is drawn toward an unlocking position to activate a maintenance unit (16) for maintaining a blocking part (11) arranged remotely from a ramp so as to allow returning of the moving part in a rear extreme position. An inertial runner (25) moves the unit in event of sudden deceleration forwardly to prevent the unit from fulfilling its maintenance function when the moving part is projected by inertia in the unlocking position so as to block the moving part during its return in a front extreme position.