PURPOSE: To produce the optimum operation schedules of many plants by satisfying the constraint in terms of time or space by means of an optimization method and based on the gene of every offspring problem and minimizing the plant operation cost.

CONSTITUTION: This device consists of an input device 1 which inputs the desired production quantity set at every time point of a day and the generation alteration number repeated by the hereditary algorithm, an output device 2 which outputs an optimum plan, a computer 3 including a CPU 4 which produces a plant operation plan of a day, and a storage 5 which stores the characteristic data and the processing procedure of every plant. Then the offspring problems are connected together in terms of time or space, so that an operation plan is produced for a source problem. Then the goodness of fit of the gene is decided for the final offspring problem based on the goodness of fit of the offspring problem, the goodness of fit of the offspring problem decided when the plan of the source problem is produced and also on the degree of satisfaction of the constraint. Thus it is possible to produce the optimum plan of the offspring problem and also to produce the optimum plan of the source problem that satisfies the constraint.