A lid-closing device has a rototranslating pin stressed by a spring, mounted in a box and having a head adapted to hook a hook of a lid, and a rocker pivoted in the box and connected to the rototranslating pin and to a heart-shaped cam. The rocker is completely rigid and not flexible and is pivoted in the box in such manner to leave clearance in order to permit the rocker to translate so that the follower of the rocker can follow the tracks of the heart-shaped cam. Springs are disposed between a lateral wall of the box and the rocker to compensate and dampen the translation of the rocker.