The device has a rigid structure (1), associated to a lawnmower, inserted in a components collecting bag (8) and supporting the bag. The structure permits to divide an inner volume of the bag into filling and air flow evacuation volumes (4, 5). The volume (4) is delimited by an air/components flow inlet panel and an air flow outlet panel. The volume (5) is delimited by the outlet panel and the walls of the bag. An independent claim is also included for a lawnmower comprising a components collecting bag filling device.