A power source terminal and a ground terminal for a semiconductor integrated circuit are connected to a conductor pattern through a capacitor. The conductor pattern is connected, through a filter, to a plane conductor connected to neither a ground plane nor a power source plane. Thus, a common mode noise arising from between the power source and the ground is caused to flow into the plane conductor. This reduces the common mode noise flowing in the ground and the power source of the printed wiring board, which relatively act as antennas.