To apply partial silver plating at a high speed on both front and rear surfaces of the inner leads of lead frames.

First and second drum type partial plating apparatus 21, 22 are arranged before and behind in a lead frame transporting direction. The respective drum type partial plating apparatus comprise rotary drums 24 which respectively have masking jigs 24b for partial plating on their peripheral surfaces, pressure belts 27 which press the lead frames on the peripheral surfaces of the rotary drums from outward and liquid injection nozzles 28 which are disposed within the rotary drums and apply silver plating only on the prescribed regions at the front ends of the inner leads by applying the plating liquid to the lead frames 12 through the masking jigs 24b. Both sides of the lead frames 12 are subjected to the partial plating treatment by bringing the one surface of the lead frames 12 into contact with the rotary drum of the first drum type partial plating apparatus 21, then bringing the other surface of the lead frames 12 into contact with the rotary drum of the second drum type partial plating apparatus 22.