PURPOSE: To facilitate the tearing of a sleeve and to prevent the blowoff of content at the time of the heating due to a microwave oven, by providing a tear strip and a tearing start notch to the predetermined part of the part corresponding from the shoulder part of a container to the upper stage of the body part thereof when the container is covered with the sleeve in a shrunk state.

CONSTITUTION: Perforations 2, 3 are formed to the predetermined part from the middle stage of the shoulder part 12 of a container 10 to the upper stage of the body part 13 thereof when the container 10 is covered with a sleeve 1 and a notch for starting tearing is further formed to the predetermined part of the tear strip 6 held between the perforations 2, 3. The sleeve 1 is allowed to cover the container 10 and passed through a heat-shrinkage process to form the container covered with the shrunk sleeve 1. After the tear strip 6 is torn and a cap is once opened, the cap part is again allowed to cover the container 10 and the whole is heated by a microwave oven. Hereupon, the skirt part 24 of the shrunk sleeve 14 allowed to cover the cap part generates secondary shrinkage to fix the cap part to a neck part. This fixing can be easily released by applying force and is a degree suppressing the blowoff of content due to the heating of the microwave oven.