A coupled portion of mutual laminate films sufficiently contributes to the formation of a packaging bag in that the coupled portion itself has excellent air tightness and liquid tightness. The tensile strength required for the laminate film is given to the coupled portion, whereby a temporary stop of a packaging apparatus is useless when a connecting portion of the laminate film is passed through the apparatus, thereby enhancing the operation efficiency and improving the yield of the material. Oriented base film layers are joined in a mitre form at the coupled portion between a rear end portion and a front end portion of laminate films comprising oriented base film layers and sealant layers.