PURPOSE: To improve the stability, airtightness of a seamed part itself by mov ing a seaming roll further toward a bottom board after a multiple seamed part is formed.

CONSTITUTION: The flange 2 of a shell plate 1 and the flange 4 of a bottom board 3 are seamed repeatedly to form a multiple seamed part 12 and, continuously, as this multiple seamed part 12 is necked in toward the center of the bottom board 3, an expanding chuck 10 is expanded to the diametral direction. At this time, the outermost peripheral part of the expanding chuck 10 is set outside the outer peripheral part of a fixing chuck 8, and a space is formed between the outer peripheral part of them and the bottom plate 3. The multiple seamed part 12 can be necked in by this space toward the center of the bottom plate 3. When the neck in is formed, the multiple seamed part 12 is held by the peripheral surface 9 of the fixing chuck and consequently excellent stability, airtightness can be secured.