PURPOSE: To make cleaning work of a inner side of a duct body easy and the structure simple by arranging recessing part on outer periphery of the duct body and incorporating a core in the recessing part.

CONSTITUTION: Proceeding magnetic field is formed at between an induction coil 4 and the core 6 incorporated in the recessing part 7 on the outer periphery of duct body 3, and induction current is conducted to molten metal 2 in a cross section U shaped flow path 8 surrounding the recessing part 7 with this proceeding magnetic field. By relative action between this induction current and the proceeding magnetic field induced with the induction coil 4, thrust is generated in the proceeding direction of molten metal 2. The molten metal 2 is traveled with this electromagnetic force and flowed in from one end of the duct body 3 and flowed out from the other end through the cross section U shaped flow path 8 at the center part.