PURPOSE: To effect a mechanically successive case packing operation of finished packages with their entrance and exit openings closed in order to improve operational efficiency, by holding nonrigid, thin commodities between supplied two-faced sheets and forming a packing bag by heat sealing the sides and bottoms of such sheets.

CONSTITUTION: A plurality of piled U-shaped packs (a) is sent from a conveyor 1 on the side of a bag forming device to between two-faced sheets 2 and 2' guided between a first supply conveyor 5 and a press and supply conveyor 6 and the two-faced sheets 2 and 2' are then heat sealed by heat rolls 11 and 11' at their sides. These two sheets are thereafter heat sealed by an upper seal bar 16 and a lower seal bar 18, their bottoms are cut off by a cutter edge 15 to form the openings thereof. A finished package (c) with the piled U-shaped packs (a) enclosed by a packing bag (a') is sent to a second supply conveyor 12, transferred onto a vertically movable plate 22 by holding its bottom with a chuck 20 and then dropped into a corrugated cardboard box (b) placed on a stand 23 by downwardly sliding said plate 22.