PURPOSE: To provide the subject method comprising the steps of: causing a magnetic force to act on a can and causing the can to tightly adhere to a die ring thereby to mold the can by a single process without generating buckling or wrinkles.

CONSTITUTION: When the upper end 10 of a can 1 comes to the lower end part 32 of the inward pursed inclined part 31 of a die ring 3, a DC current flows to a coil 4 by the command of detection means. The die ring is magnetized and converted into a magnet and acts to cause the can 1 made of a magnetic metal material to tightly adhere to the die ring 3. When the opening end 10 of the can 1 further advances along the inner peripheral surface and the die ring 3 comes to a position where the necking is completed, the current which has flowed through the coil 4 by the command of detection means which detects the relative position is cut off. The can is separated from the necking device and discharged therefrom.