To prevent a once shrunk container main body from stretching again, reduce the volume, and facilitate the disposal by a method wherein a stretching/shrinking means which stretches/shrinks the container main body in the height direction, is formed, and on the external surface of the container main body, a recesses part for fitting and a protruding part for fitting, which is fitted in the recessed part for fitting by a male-female engagement, are formed on the top and the bottom so as to be confronted with an interval.

On a container main body 1, a bellows 6 is formed, and continuing from a shoulder part which is connected to a container mouth (1a), a recessed part piece 8 equipped with a recessed part 3 for fitting, is formed on the external surface of the container main body 1, and at the same time, a protruding part piece 7, for which a protruding part 4 for fitting is formed, is formed so as to be confronted with the recessed part piece 8. By such a constitution, the container main body 1 can be shrunk by the bellows 6, and by fitting the recessed part 3 for fitting and the protruding part 4 for fitting by a male-female engagement, which are formed on the external surface of the container main body 1, the shrunk state of the container main body 1 can be surely maintained, and the once shrunk container main body 1 is prevented from stretching. Therefore, a 'degassing' of carbonated beverages can be prevented from generating, and the most shrunk state of this packaging container A can be maintained for the disposal.