To shut off the open air so as to hold gas compsn. exhibiting CA keeping effect by forming a group of belt-like scars extended on the trunk part of a bag in the transverse direction and forming notches whose lengths are longer than the widths of this group of belt-like scars so as to position their length directions at a specified angle to the transverse directions.

A packaging bag 1 is formed of a polyolefin resin film and is sealed at a seal part 4 and a group of belt-like scars 3 extended on the trunk part 2 in the transverse direction is provided. This group of belt-like scars 3 is formed in such a way that a plurality of lines of the groups of the belt-like scars are arranged so as to make their length directions positioned at an angle of 90±20° to the directions transversely intersecting the trunk part 2. E.g. notches 6 are formed in such a way that the lengths are of the order of 0.1-1.0 mm and the widths are of the order of 1/10-1/100 of the length and in a staggered arrangement. The packaging bag 1 like this can be easily opened by pinching the film of the part where the groups of the belt-like scars 3 are provided and pulling it to the left and right.