PURPOSE: To make unsealing posible for a bag with a small force without allowing the bag to be torn by a method wherein an unsealing part is formed with edge lines on both ends of a bag-forming film placed adjacently, and a release tape is welded for sealing along two welding lines over the unsealing part.

CONSTITUTION: A seal-up bag 1 is made of a film that is made up with its both sides formed of heat sealing layers 10. An unsealing part 2 is formed with edge lines 3 on both ends of a bag-forming film placed adjacently, pr contacting or overlapping each other. A release tape 4 is welded for sealing, extending over the edge lines 3 on both ends. Heat sealing layers 11 are formed to both sides of the release tape 4 while a separate layer 12 is formed to the inside thereof. Two welding lines are provided to the outside of each of the edge lines 3 on both ends of the bag-forming film. Welding is applied to welding parts 6 on both the upper and the lower ends of the seal-up bag 1 with unwelded parts 7 left unwelded on both the upper and the lower ends. Therefore, the release tape 4 is made to be unstuck on the welded parts 7, allowing tabs 8 to be formed for being caught by fingers. By nipping and pulling the tabs 8 with the fingers, the relase tape 4 can be splitted in the separate layer 12, and unsealing can be made with the two edge lines 3 closed with the release tape 4 opened.