A blow molding mold is adapted to be mounted to a blow molding device and having a cavity surface. The blow molding device has a pressurized liquid supply function of supplying a pressurized liquid to stretch the preform toward the cavity surface and also has a head space defining function of defining head space in the container by drawing back a part of the liquid filled into the container through a blow nozzle or by withdrawing a stretching rod from the container filled with the liquid. The cavity surface includes a bottom forming surface, a trunk forming surface, a shoulder forming surface, and a mouth forming surface, and the trunk forming surface includes a flattened portion that, in the transverse section, has a flattened shape.

Ways for controlling a level of a product in a container are provided that include engaging an exterior surface of the container containing the product at a first product level. A force is applied to the exterior surface of the container to cause the container to change from a first volume to a second volume. Cessation of the force results in the container containing the product at a second product level. The second product level can provide an accurate and reproducible final product level in the container.

Ways for controlling a level of a product in a container are provided that include engaging an exterior surface of the container containing the product at a first product level. A pulling force is applied to the exterior surface of the container to cause the container to change from a first volume to a second volume. Cessation of the force results in the container containing the product at a second product level. The second product level can provide an accurate and reproducible final product level in the container.

A method for manufacturing a double-wall container includes a blow molding process of forming an intermediate molded body by blow molding, the intermediate molded body including a projection part that is provided at a boundary portion between an inner wall forming part and an outer wall forming part and projects outward in a radial direction of the outer wall forming part; an inverting process of pushing the inner wall forming part inside the outer wall forming part and inverting the inner wall forming part, thereby forming the intermediate molded body into the double-wall container; and a collapsing process of collapsing the projection part in a depth direction of the intermediate molded body to form a crease at the boundary portion between the inner wall forming part and the outer wall forming part, the collapsing process being performed before the inverting process.