A capacitor arrangement assisting method wherein data entered by a user, such as the width w of a power supply wiring, the thickness h of a dielectric between the power supply wiring and a ground plane, the ESLcap of a capacitor, and a target frequency fT and a target impedance ZT of an IC, are received, the maximum allowable wiring length lmax of the power supply wiring is calculated on the basis of the received width w of the power supply wiring, the thickness h of the dielectric, the ESLcap of the capacitor, and the target impedance ZT of the IC at the target frequency fT, and the calculated maximum allowable wiring length lmax is displayed.