Abstract: A multi-bag comprises a multi-film made by superposing at least an inner film and an outer film and sealing the cylindrically curved superposed region to form a back seal. The multi-film constituting the multi-bag is a double film formed by flattening a tube-like film into a two-layer form, with the opposite end edges, which are parallel with the direction of extrusion, continuing to each other. The multi-bag is formed in a sealed state by a back seal, a planar seal at one end, and a planar seal at the other end. The supply system for the multi-film may be such that one system is prepared for each double so as to simplify the device. Further, in the film supply process, it is possible to obtain a multi-bag of high quality without applying a shift-preventive means to between the multi-films.