In this paper, we propose an efficient scheduling method for a job shop environment in which production capacity is adjustable by adding overtime in each machine of each production shift. The primal objective of scheduling is to meet due-dates of jobs and the secondary one is to minimize overtime. To achieve these two objectives efficiently, the schedule is searched to eliminate tardy jobs at first by allowing large overtime. Then the overtime is minimized. The method using the mixture of

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... c algorithm and priority rule is applied for this scheduling. In this method, the characteristics of priority rules are the key for improving performance. In particular, when minimizing overtime after finding schedules without tardiness, it is important to maintain more individuals meeting due dates even after genetic operations are applied. For this purpose, we propose a scheduling method using the priority rules which are modified (CR+SPT) rule and ATC rule. Numerical experiments show the effectiveness of the proposed method.