In this letter, integrated optimization system, a new framework of practical optimization, is expanded to multi-objective optimization problem. This system is used in order to reduce the number of accesses to a simulator. On the basis of simulation results using some typical benchmark problems, it is shown that the proposed integrated optimization system enables to obtain relatively good Pareto solutions with drastic reduction in the number of function calls for evaluating the performance index values of systems. Copyright © 2010 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.