Abstract: There is provided with a clock timing adjusting method for adjusting the difference of clock timings among a plurality of clock domains in a semiconductor integrated circuit which includes a clock generation portion capable of supplying a plurality of clocks with different phases, a plurality of clock domains for supplying clocks supplied from the clock generation portion to corresponding flip-flop groups, respectively, and a logic circuit portion having the flip-flop groups. In the clock timing adjusting method, a latency of each of the plurality of clock domains is extracted, then the phases of clocks supplied to the clock domains are determined among the plurality of clocks generated from the clock generation portion based on the extracted latencies, and the number of clock buffers is determined in order to adjust a latency difference of the plurality of clock domains which can not be adjusted by the determined clocks.