PURPOSE: To stretch enclose a mid-partition plate in the can opening by mainly press- working only and seal the opening, by constituting a double wall by inserting the can opening edge into th inside, and also heat-depositing the press-contact part of the curved part of the can opening edge and the mid-partition plate.

CONSTITUTION: A seal die 2 is inserted into prescribed height of the inside of a can body 1, and after that, a mid-partition plate 3 is placed on the die 2 temporarily, the circumferential edge of the plate 3 is curved upwardly and it is made to press-contact with the inside wall of the can body. Subsequently, to the can opening edge of the can body 1, a curl forming recessed groove 4a of a curl punch 4 is made to press-contact, and after that, pressure is reduced, and the can opening edge is curved to the inside by the groove 4a. Subsequently, the punch 4 is made to further descend, a curved part 8 is made to descend while forming a double wall by the can opening edge and its lower end part is made to press-contact with the plate 3. Subsequently, a circumferential edge part 7 of the plate 3 is pressed and pinch-stuck between the die 2 and the curved part 8, the die 2 is heated to a prescribed temperature by a heat source 9 embedded in the die 2, and the plate 3 and the curved part 8 are thermally deposited. In this regard, 10 in the figure denotes a heat-resisting material which covers the inside wall and a part of the upper wall of the die 2.