To save resources by not damaging or tearing a paper bag in opening and by using the bag repeatedly.

Of the outside face of the back face section 2b of a paper bag body 2, the area laying along the tip end side 3a of a flap 3 when the flap 3 is folded back is provided with the first paper protection layer 5 and the area which lays along the tip end side 3a of the flap 3 of the outside face of the flap 3 when the flap 3 is folded back is provided with the second paper protection layer 6. An adhesive tape 7 can be attached to the layer 5 and the layer 6 causing no damage to them when the tape is removed. In sealing, the tape 7 is attached to the layers 5, 6 covering both layers 5, 6 but not covering the area where the layers 5, 6 do not exist and the flap 3 is stuck to the front face 2a of the body 2 for sealing.