PURPOSE: To make it possible to rapidly set cores in a drag without damaging these cores.

CONSTITUTION: This method for housing the cores consists in acting repulsive force between magnetic materials 8j, 9j provided in core print parts 8h, 9h of the cores 8, 9 and electromagnets 40, 42 provided in a core print supporting part 4h of the drag 4 in the process of fitting the core print parts 8h, 9h of the cores 8, 9 into the core print supporting part 4h of the drag 4. The repulsive force consequently acts as a buffer even if the core print parts 8h, 9h and the core print supporting part 4h are rapidly fitted by rapidly lowering the cores 8, 9 with respect to the drag 4 and, therefore, large impact is not applied to the bodies of the cores 8, 9 and the core print parts 8h, 9h. The cores 8, 9 are thereby rapidly set to the drag 4 in the state of not damaging the cores 8, 9.