Self-standing bag and method and device for making said bag

A self-supporting bag comprising a part constituting the trunk and a part constituting the bottom both made of a multilayer plastic film comprising a heat adhesive plastic layer as the inner layer thereof is provided. The inner layer or the outer layer of the multilayer plastic film of the part constituting the trunk has a section comprising convex parts and concave parts adjacent with each other. The linear ribs are formed by pressing a positive mold having linear protrusions at the top face against the multilayer plastic film to form linear troughs on the film with decrease of the thickness of the pressed part of the film and a raised part at the upper edges of the troughs on the film and by fixing the raised parts on the film.