To provide a magnetic flux generator for a method for an electromagnetic welding which is a new seam welding method.

In the equipment with which a high density magnetic flux is rapidly applied on stacked sheet metals using a coil for generating the magnetic flux and the sheet metals 5 are seam-welded by making use of a generated eddy current and an electromagnetic force, the coil for generating the magnetic flux is composed of a secondary coil 10 of a transformer for welding. Further, the secondary coil 10 of the transformer for welding is divided into two parts; each divided secondary coil is independently connected to the coil for generating magnetic flux on the side of one of sheet metals and to the coil for generating magnetic flux on the side of the other sheet metal. The equipment is characterized by the fact that the magnitude of magnetic flux density generated on each stacked sheet metal is independently variable when the seam welding is performed for stacked sheet metals 10 of the same kind or different kinds by using the equipment.