PURPOSE: To efficiently execute a search, and also, to secure a discovery of an optimal solution by searching a state space in the utmost diving direction, and increasing an evaluation function value of the minimum solution in the case it reaches the minimum solution.

CONSTITUTION: From various combinations in a state space being an aggregation of a state of each combination, the best combination is discovered and optimized. In this case, the state space is searched in the utmost diving direction in which an evaluation function value decreases to the utmost, and when it reaches the minimum solution, and cannot continue the search in the utmost diving direction, the evaluation function value of its minimum solution is increased, and the search in the utmost diving direction is executed continuously again. That is, since the search of the state space is executed in the utmost diving direction, a solution of a good quality can be discovered in an early stage of the search. Also, since the search is continued increasing the evaluation function of the minimum solution, the discovery of an optimal solution is secured by taking large enough the number of times of the search.