To overcome the problem that the following gases or moisture should be removed to the outside of the bag because carbon dioxide, or an added enzyme and so forth are generated through the respiration of a food in the bag, spoiling the quality of the food in packaging bags of fresh foods, or processed foods.

A synthetic resin film is thinned down to a thickness of 5 to 70 μm by pressing or stretching at a specified position. The thin film section is stretched or expanded by the gasses such as carbon dioxide or moisture which are generated by the content because the thin film section is thinner than other sections. This food packaging bag has a structure wherein the gas or moisture escapes from the thin film section which is even thinner at this time. The food packaging bag of this constitution is provided.