PURPOSE: To simply put in an ornamental body, such as a bouquet or the like by a method wherein a cylindrical opening part on which the neck part of a balloon is mountable, is provided with either of a pair of box pieces, which form a chamber by incorporation.

CONSTITUTION: A bag part 12 of a balloon 1 is put in a box piece A through its cylindrical opening part 21, and then a neck part 11 of the balloon 1 is folded back and is put on the rim of the opening part 21. Air is supplied into the bag part 12 at the neck part 11 of the balloon 1, which is put on the opening part 21 of the box piece A, and the air expands the balloon. While the neck part 11 is being sealed, both the box piece A and a box piece B are incorporated with flanges 22, 23, and are fixed with camps P. A chamber C in an air-tight state is formed and the air in the balloon 1 acts on the balloon so that the air pressure in the chamber C is kept as it is, and hence the air in the balloon is not exhausted even if the sealing of the neck part 11 is removed. When a bouquet F is put in through the neck part 11, which is put on the opening part 21 and is opened, the bouquet F can be easily put in the bag part 11 of the balloon 1.