Paper bag

A paper bag comprising:

• a paper bag body, one end of which is closed with a closure flap that is equipped in a gusseted tubular trunk part such that a portion of the closure flap protrudes from an edge or edges of one end and/or another end of the trunk part, said closure flap closing said one end to form a bottom part of the bag, or closing said another end being used as an opening through which the paper bag body is filled with a content after the content is filled through the opening;
• a non-water-soluble hot-melt adhesive that is coated on a surface of said portion of said closure flap that protrudes from the edge of said paper bag body;
• and
• an underlining paper piece that is adhered in advance with a water-soluble adhesive to a part of one wall surface of said paper bag body that overlaps the closure flap when said closure flap is folded along with said end of the paper bag body and is adhered to said wall surface by reactivating said non-water-soluble hot-melt adhesive,
• wherein, said underlining paper piece can be peeled from said wall surface of said paper bag body or can be peeled away between layers of said underlining paper piece.