A semiconductor integrated circuit device (100) is provided with data outputting buffers (310.1 to 310.j) for respective data input-output terminals. Each buffer (310.i) is supplied with a power supply potential and a grounding potential from a power supply wiring and two systems of grounding wiring connected to independent power supply pads and grounding potential supply pads, respectively. When the device (100) outputs a signal of "H" level, each data outputting buffer supplies an electric current to the corresponding data outputting terminal through the two systems of power supply wiring. Therefore, the current flowing through each system of power supply wiring is suppressed and the noise generated in the power supply wiring and in the grounding wiring is reduced.