This disclosure concerns a semiconductor circuit design method for designing a clock wiring structure supplying a clock to a flip-flop by using a computer. The semiconductor circuit design method comprises setting the flip-flop based on circuit information on a semiconductor integrated circuit; obtaining a control signal controlling the flip-flop; calculating a first evaluation value indicating a power consumption and a magnitude of a clock skew time when clock gating is applied to the flip-flop; setting a gated clock structure clock-gating the flip-flop when the first evaluation value is higher than a first threshold; calculating a second evaluation value indicating the power consumption and a magnitude of a cell area when a low power flip-flop lower in power consumption than the flip-flop is applied to the flip-flop; and replacing the flip-flop by the lower power flip-flop when the second evaluation value is higher than a second threshold.