Abstract: A plurality of clamps arranged in equally spaced relation on an endless track are intermittently advanced at a pitch equal to the distance of each two adjacent clamps. A switch reactive only to the passage of a sufficiently heavy or filled bag which has been filled with an article is disposed downstream of a filling station, one of the stop positions for clamps. When the passage of a bag is not responded by switch, that is, when an empty or unfilled bag has passed near the switch, the particular clamp by which the empty bag is held is caused to pass through the final stop position and, in turn, through the first stop position before it can again reach the filling station, with the empty bag being held by the clamp all the while.