PURPOSE: To form a plating film of a favorable crest shape by relatively specifying the shape and disposing position of plating solution jet port to a surface to be plated.

CONSTITUTION: An aluminum material 18 is previously formed on the front surface of the side to be plated of an insulating board 17, and a resist mask 19 is disposed at a predetermined position on the material 18. Aluminum plating solution is continuously supplied in a large quantity to the surface to be plated of the board 17 along a direction of an arrow A from a plating solution supply port 12, and circulated to a separately installed spare plating solution tank. A plating range is specified by the shape of the mask 9, a push plate 20 is placed to be pushed on the board 17 to conduct the material 18 while preventing leakage of the solution. If the collision speed of the solution to the surface to be plated is suitably selected, a common electrode raised at the center of a plating film M can be formed. After plating, a plated component is washed, remaining solution is removed with ammonia water or the like, further washed, dried and used as a common electrode of a thermal head.