Upon detecting that a point that satisfies a predetermined condition and whose distance from a reference point is shorter than a distance from the reference point to a first point obtained by searching a parameter space based on values of a first search indicator under a first constraint exists in the parameter space, a second point is calculated under the first constraint in the parameter space by a search method other than the searching using the first search indicator. Then, generating a second search indicator represented by a first linear combination of at least certain of first search indicators so as to obtain the second point or an adjacent point of the second point, when searching by using the second search indicator or generating a second search indicator so that search is carried out in a direction of the second point when using the second search indicator is carried out.