PURPOSE: To prevent a metal from adhering to the vicinity of the surface of a welding zone, improve the flatness of the surface of the welding zone and reduce the deposit quantity of chrome carbide caused by the reduction of the heat input quantity by arranging a means for applying a magnetic field having a component vertical to the surface of the welding zone.

CONSTITUTION: In the welding device for connecting plural members by melting the respective welding zones of plural members, by forming a magnetic field having a component vertical to the surface of the welding zone by using permanent magnets 102, 102', etc., metallic fume generated at the time of welding is left in the welding zone, the flow to the downstream side of a welding construction part is prevented, and it is prevented that the metallic fume is deposited onto a member to be welded. Also, as for a metallic melt, electric conductivity is high, therefore, the average property of the welding zone is improved by a magnetic field. Moreover, since the magnetic field can converge ions or electrons generated by a melting means, a beam can be narrowed down, and welding bead width can be finished narrowly.