Abstract: A device for closing boxes which are each provided, at least one end face, with at least one flap with a complementary end flap and with at least two folding lateral tabs which mutually interlock in the closure configuration with the complementary end flap, comprising, arranged laterally with respect to the direction of advancement of the boxes and one after the other, a folding element for folding the flap with respect to the box, at least one first rotating element for folding the complementary flap with respect to the flap, at least one second rotating element for inserting the complementary flap in the mouth of the box, and at least one third rotating element for interlocking the complementary flap with the lateral tabs, to completely close the box.