A bag evacuation valve mechanism which can be used with suction devices having suction nozzles of different diameters and does not damage tightly closed bag stacked thereon to form a flat and stable shape of packing. A suction connector attached to the outer surface of a bag having a hole formed therein, and having a vent formed in its center has a generally flat shape, and a valve base on the inner surface of the bag has a recessed shape in cross-section. Such a valve mechanism can be used with suction devices having different nozzle diameters by placing the nozzle in contact with the suction connector to covering its vent, and as it has no projection on the outer side of a tightly closed bag, it does not damage any other, for example, tightly closed bag stacked on its outside or placed adjacent to it.