a robot or the like it is moved into a heated recess 5 of a movable solder bath 4 filled with a molten first solder alloy 3 the frame 2 is moved horizontally 7 while the lower ends of the corrugate fin 1 are dipped in the molten first solder alloy 3 and the lower ends are in a friction state with a bottom surface of the recess 5 and the first plating of the molten first solder alloy 3 is applied onto the lower ends of the corrugate fin 1 furthermore the above step 3 is replaced with a step 3a wherein a second solder alloy 9 is heated and molten on a base plate 8 made of one of cu a cu alloy al and an al alloy a metallic brush 12 is brought into contact therewith the base plate 8 is manually or mechanically moved in a horizontal direction to rub the base plate 8 with the metallic brush 12 and the second plating of the molten second solder alloy 9 is applied thereto next in a manufacturing method of a radiator according to another embodiment of the present invention the above step 2 or 2a is replaced with a step 2b wherein in fig1 a flux is applied to the lower ends of the corrugate fin 1 fitted in the frame 2 it is heated and the first plating of the first solder alloy 3 is applied onto the lower ends of the corrugate fin 1 next in a manufacturing method of a radiator according to another embodiment of the present invention the above step 3 or 3a is replaced with a step 3b wherein in fig1 a flux is applied onto a base plate 8 made of one of cu.