Abstract: A printed wiring device includes an insulation layer, a base layer, i.e. grounding layer or power supply layer, disposed on the insulation layer, and a signal line disposed on the insulation layer at the opposite side of the base layer. A plurality of holes is formed in the base layer opposite to the signal line, so that an average capacitance value between the signal line and the base layer is decreased. Thus, even if the insulation layer is thinned without narrowing the width of the signal line, characteristic impedance of the signal line can be controlled at a desired value.