When a design apparatus adjusts clock skews, the design apparatus separates each of the power supply currents which flow through circuit sections that operate in synchronization with a clock signal into a plurality of frequency components, sets skew values of the clock signal which reaches the circuit sections, and performs, by changing the skew values, repetition of calculating a combined amplitude by combining, with respect to each of the frequency components, corresponding ones of the frequency components of the power supply currents which flow through the circuit sections and finds dependence of the combined amplitude on a skew.