PURPOSE: To make switching noises small, by providing a plastic IC with a metal lead of a structure wherein the lead is branched into a plurality of leads in seeling plastic, the leads of the metal lead part are bonded, and said metal lead part and a piece of a metal lead part outside the sealing plastic form a unitary body.

CONSTITUTION: An inner metal lead 2 for GND at the end pin of a plastic IC is branched into parts 2 and 7. At the same time, e.g., on a mask pattern, a GND line is branched into a GDN line 11 for an output circuit system and GND lines 12 for an input circuit system and an inner circuit system. Therefore, even if switching noises are inputted into a GND pad 5 of the output circuit system, only the small noise is inputted in a GND pad 9 in the input circuit system. When the length of the metal lead 2 from a mounting point 10 on a board to the branching point of the inner metal lead is l1 and the length to the tip of one inner metal lead 2 is l2, the noise that is inputted in the GND pad 9 in the input circuit system is expressed by vl1/l2. Therefore, the GND noise v' in the input circuit system can be made very small by adjusting l1.