To reduce an excessive stress action to a packaging case by a method wherein the mutual speed between the surfaces to be caulked of the case, which is held by a chuck and is rotated, and the caulking surfaces, which come into contact with these surfaces to be caulked, of caulking top is made zero or is brought close to zero to perform a cauling treatment.

A packaging case 4 is held by a chuck 6 and a rotary mechanism 8 of a rotating means is coupled with the chuck 6 via the axis of rotation of tha chuck 6. Moreover, a first caulking top 10 and a second caulking top 12 are provided on the side of the opening end of the case 4 as two rotationally molding means and rotary mechanisms 20 and 22 are respectively coupled with each of the tops 10 and 12. In this state, the tops 10 and 12 are rotated while being controlled so that the speed of the peripheral surface of the caulking surface 26 of the top 10 or the caulking surface 28 of the top 12 and the speed of the peripheral surfaces of the surfaces P and Q to be caulked of the case 4 become the same speed, that is, the relative speed between both surfaces of the surfaces 26 and 28 and the surfaces P and Q becomes zero to contrive to perform a caulking treatment. As a result, an excessive stress action to the case 4 can be reduced.