PURPOSE:To make it possible to reduce extremely effectively noises to other electronic equipments by employing simple constitution only with a high resistance inserted into a signal line. CONSTITUTION:Units 1 and 2 of a vehicle digital equipment are mutually connected at output terminals O1 and O2 and input terminals I1 and I2 via signal lines 3-5. Further, signal lines 3-5 have high resistances R1-R3 (resistance value; 1-10KOMEGA) provided in series near terminals O1 and O2. Car-body harness used as signal lines 3-5 naturally has its distributed capacity (200-500PF), interline floating capacity and reactance, and constitutes distributed constant circuit X, and a RLC filter is formed of this circuit X and high resistances R1 and R3. As a result, when a digital signal of signal frequency band 500Hz-1MHz is transmitted, only the higher harmonic components of the digital signal is effectively attenuated, so that the radiation of noises from those signal lines can effectively be suppressed.