A container is formed by a blow molding method in which a cylindrical parison made of a single layer or multilayer resin material is inflated by air while heated inside a mold. A bottom seal section formed by a pinch-off portion of the mold has a portion projecting outside the container, and one of the resin layers constituting this projection bites into the other resin layer to form a bite portion. Accordingly, the fusion strength can be increased by increasing the fusion area between the resin layers, and the bite portion increases the strength against shearing force parallel to the fusion surface.
