At least two carrying cases , each comprising: a flat top surface ; a flat bottom surface , the flat top surface and the flat bottom surface being aligned in a first direction (Z direction); two top surface rib grooves extending in a second direction (X direction) perpendicular to the first direction (Z direction) and recessed in the first direction, on the top surface ; and four interfering projections projecting in the first direction (Z direction), on the bottom surface , wherein each of both ends of one of the top surface side rib grooves seen from the second direction (X direction) has an inclining portion which is inclined toward one side in a third direction (Y direction) perpendicular to both the first direction (Z direction) and the second direction (X direction), each of both ends of the other top surface side rib groove seen from the second direction has an inclining portion which is inclined toward the other side in the third direction (Y direction), the respective interfering projections are disposed at positions corresponding to the respective inclining portions such that the respective interfering projections are in contact with the respective inclining portions of the respective top surface rib grooves from the inside thereof when said at least two carrying cases are piled up in the first direction with the top surface of one case placed on the bottom surface of the other case, and the respective interfering projections have dimensions accommodatable in the top surface rib grooves in the third direction (Y direction) and are formed by a combination of a plurality of long and thin projecting strips . a flat top surface ; a flat bottom surface , the flat top surface and the flat bottom surface being aligned in a first direction (Z direction); two top surface rib grooves extending in a second direction (X direction) perpendicular to the first direction (Z direction) and recessed in the first direction, on the top surface ; and four interfering projections projecting in the first direction (Z direction), on the bottom surface , wherein each of both ends of one of the top surface side rib grooves seen from the second direction (X direction) has an inclining portion which is inclined toward one side in a third direction (Y direction) perpendicular to both the first direction (Z direction) and the second direction (X direction), each of both ends of the other top surface side rib groove seen from the second direction has an inclining portion which is inclined toward the other side in the third direction (Y direction), the respective interfering projections are disposed at positions corresponding to the respective inclining portions such that the respective interfering projections are in contact with the respective inclining portions of the respective top surface rib grooves from the inside thereof when said at least two carrying cases are piled up in the first direction with the top surface of one case placed on the bottom surface of the other case, and the respective interfering projections have dimensions accommodatable in the top surface rib grooves in the third direction (Y direction) and are formed by a combination of a plurality of long and thin projecting strips . <EOS>