A first model expression having a first order and representing a relationship between evaluation indicators and the design parameters and a second model expression having a second order higher than the first order and representing a relationship between them are generated. Then, according to a quantifier elimination method, values of the design parameters, which realize an optimum solution of the first model expression, are calculated. And, a design parameter whose value is identical to an upper limit value or a lower limit value is identified, and the second model expression is transformed by substituting the upper limit value or the lower limit value, as a value of the identified design parameter, for the second model expression. Finally, according to the quantifier elimination method, values of the design parameters in the transformed second model expression, which realize an optimum solution of the transformed second model expression, is calculated.