PURPOSE: To completely prevent a plating liquid from entering a place requiring no plating, by providing a second pressing plate on the lower surface of a pressing plate bonded on the lower surface of a pressing jig positioned above, and by providing a protuberant portion on the upper surface of a mask positioned below.

CONSTITUTION: A protuberant portion 13 having substantially the same thickness as a lead frame 1 is provided around a plating liquid jetting orifice 6a on the upper surface of a mask 6 bonded and fixed on a jig 7. On the other hand, a second pressing plate 14 having an area somewhat larger than the region of the lead frame to be plated is bonded on the lower surface of a pressing plate 7 by means of sponge rubber being softer further than sponge rubber forming the pressing plate 8. When the lead frame 1 is pressed by a pressing jig 9, the second pressing plate 14 having a smaller area presses intensively the region to be plated, fully introducing into a punched portion 4 of the lead frame 1. Meanwhile, the protuberant portion 6a of the mask 6 also intrudes well into the punched portion 4 of the lead frame 1, and thus a jetted plating liquid 12 is prevented completely from invading into a region other than the region to be plated.