Abstract: A posture corrector device (1) that is arranged on the lumbar region and that includes a generally U-shaped stiffening inner structure (2) that remains housed within an external cover (3) that possesses wings (5) at its end. Preferably the wings (5) are foldable with respect to the central part of the device by means of folding lines (6) and the inner face of the wings possesses a pad (4) to rest the forearms. Also, a rucksack is provided that includes a foldable posture corrector device (1) determined by the existence of respective foldable wings (5) on both sides of the rear part (11a) of the bag (11) to support the forearms and forcing the user to straighten his back when he is wearing the rucksack (10).