A reinforcement device for the casing of an awning box and a reinforcement system for an awning box, particularly those in which the box of the awning is inclined at an almost vertical angle and is intended to serve as a reinforcement to improve the closure of the load bar when it approaches the casing to close the box. The reinforcement device prevents the deformation sustained by the upper and lower profiles of said casing mainly in the center portion thereof, and especially in very long awning boxes, therefore facilitating the correct incorporation of the arms therein and the complete protection of the awning inside the box.