the nearest to wall plate shaped member a1 can be completely separated from the other plate shaped members a and consequently only the nearest to wall plate shaped member a1 alone can be conveyed to the next processing step y accurately at one time moreover the leaning force exerted by the other plate shaped members a toward the wall surface 112 side can be mitigated by the leaning force mitigation member 200 so that the nearest to wall plate shaped member a1 can be conveyed to the next processing step y smoothly by only a small force without damaging the nearest to wall plate shaped member a1 consequently in a case the plate shaped members a are corrugated cardboards it is also possible in this embodiment to prevent the crushing of the corrugation on the corrugated cardboards during the conveying operation furthermore in this embodiment the leaning force mitigation member 200 completely separates the nearest to wall plate shaped member a1 from the second nearest to wall plate shaped members a2 consequently even when each of the plate shaped members a incorporates a step portion aa as shown in fig1 due to the overlapping or slit portions ab as shown in fig1 for forming lid part of the cardboard box for instance or else each of the plate shaped members a has hooks or staplers attached thereon it becomes possible to prevent the conveying of the nearest to wall plate shaped member a1 from being obstructed due to the accidental engagement of any of the step portion aa slit portions ab hooks or staplers as well as the damaging of the nearest to wall plate shaped member.