PURPOSE: To form a synthetic resin film on a part of a metallic member by a small-size heater without providing a large-size atmospheric furnace or the like.

CONSTITUTION: A metallic member 9 is moved at a predetermined speed by a conveyor 8. A part 99 of the metallic member 9 in the course of movement is heated to approximately 300°C by a preheating device 2 consisting of a burner or the like. Powder 1 of a thermoplastic synthetic resin material is made to adhere (weld) to the heated part 9. The aforesaid synthetic resin powder 1 is supplied from a supply device 5 consisting of a screw pump 55 or the like to adhere thereto. The part with the thermoplastic synthetic resin material 1 adhering is again heated to approximately 250°C by a post-heating device 3 consisting of a burner or the like, whereby the thermoplastic synthetic resin material 1 can be uniformly fused all around. The uniformly fused material 1 is naturally cooled by a cooling part 7.