The present invention is provided with a transmission line element having a ground wiring and a power supply wiring formed interposing an insulating film, on the power supply wiring on a semiconductor chip, lead or printed-circuit board, such that the capacitance per unit length of the transmission line element is boosted to set the characteristic impedance of the transmission line element for the high frequency range to an optimum value. In this way, the power supply wiring inclusive of the transmission line element can have a satisfactory decoupling performance.