An outer container is detachable mounted on a neck of an inner container having its interior previously sterilized and sealed with a portion of the inner container underlying the neck being sealed. Such container assembly of double structure is sterilized and dried, then transferred into a germ-free filling chamber isolated from the atmosphere here the top of the inner container is cut off, then the inner container is filled with food or drink and the cut off portion is sealed again. Finally the outer container is separated from the inner container outside the germ-free filling chamber.