To easily reuse an envelope, without being noticed that it has been reused.

A left piece 3 and a right piece 4 are connected outwardly to the two facing sides of a substantially rectangular front face piece 2 and are folded back with the end of which being separably connected. A back piece 5 is connected outwardly from one of the other sides of the piece 2 and is folded back with the pieces 3, 4 in between. A sealing piece 6 is connected outwardly to the remaining one side of the piece 2 and is folded back to be adhered to the back piece 5. In reuse, the piece 6 is removed from the piece 5 to be folded to the opposite side, the pieces 3 and 4 are reconnected to each other, and the piece 6 is attached to the piece 5. Because the envelope is turned over when reusing it, the appearance of the envelope is not spoiled.