A power domain is automatically generated.A computer performs a function simulation process 9 for evaluating whether or not a designed circuit satisfies a specification, and a clustering process 10 which obtains a power domain by clustering logical blocks in which activation timings are within a range, based on the result of the function simulation process. Since the power domain is obtained by a process performed by the computer, the power domain can be optimized compared to a case when it is obtained by hand (manual work of the designer).