A power source terminal assembly for wiring of electronic instruments, in which a plurality of terminals screw rods (11a, 11b), each having a flange (31) centrally thereof, are molded into an insulation substrate (12) with the flanges partly embedded therein. At least one of the terminals (11a) screw rods is designed so that one side of the flange (31) may project outwardly from the substrate surface by a predetermined size, and this terminal screw rod (11a) is used as a grounding terminal. A casing (4) of an electronic instrument has made therein a hole (5) for receiving the grounding terminal screw rod (11a) to permit one side of its flange (31) to make contact with the casing (4) and a window (8) for insertion of the other terminal screw rods (11b) without making contact with the casing. The power source terminal assembly is engaged with the casing (4) and the grounding terminal (11a) and one portion of the power source assembly are fixedly retained by fixing means to the casing.