To shorten a working time and to enhance workability without relying on the skillfulness of a worker by providing a press means for pressing a folded- back mouth fold part to bond the same and bringing the press means to a synchronizing state with respect to the collecting pawl and jaw plate of a bonding drum.

A delivery roller 26A includes a plurality of press pads 26a pressing a mouth fold part between the roller 26A and the outer periphery of a bonding drum 21, the catching pawls 26b grasping the front side in the feed direction of bag paper and a synchronizing setting means capable of positionally setting the press pads 26a with respect to the catching pawls 26b at the position in the peripheral direction of the delivery roller 26A. The catching pawls 26b grasp the front side in the feed direction of the bag paper between the pawls 26b and the outer periphery of the delivery roller 26A in the same way as catching pawls 21c. A press roller 26E presses the mouth fold part by press pads 21c and connected to the delivery roller 26A by a synchronizing setting means 26G achieving the synchronism with the rotation of the delivery roller 26A.