To integrate a notification piece with a sealed letter again, after taking out a booklet from the sealed letter with the notification piece enclosed therein.

After a sealed letter 1 has been dispatched from a counterpart, a cutting off frame 41 is cut off from the sealed letter 1 using a cutting off sewing machine 31 to form a storage unit 42. Then, the storage unit 42 is widely opened and a booklet 2 is taken out. When desired to integrate the storage unit 42 with the booklet 2 again after the booklet is taken out, a raised portion 22 of the booklet 2 is turned around and drawn out, and inserted into a cut part 34 formed in the storage unit 42. Finally, the storage unit 42 is folded and stored in a predetermined bookshelf or the like.