Abstract: Printed circuit board 1 on which LSI2 is mounted comprises first capacitors 4a and 4b for electrically connecting power source terminals 3a and 3b to via holes 8b, first power source wiring 5a, second power source wiring 6a and a second capacitor 7a. In a predetermined frequency range, the characteristic impedances in power source wirings 5a and 6a are set to three times or more higher than the impedances in capacitors 4a, 4b and 7a. In addition, the lengths of power source wirings 5a and 6a are set to equal to or larger than a value obtained by multiplying 20 mm by the wavelength reduction rate of the printed circuit board and equal to or smaller than a value obtained by multiplying one quarter the wavelength at the upper limit frequency in the predetermined frequency range by the wavelength reduction rate.