Many companies want to build a better production schedule for efficient production-inventory management and on time delivery. Thus, they have installed commercial Advanced Planning and Scheduling (APS) systems to ERP system for better production scheduling. However, it is very difficult to perfectly apply the APS to specialized manufacture environment, and it needs to be highly customized for using it. In addition, it is difficult to expect good performance in scheduling if scheduling operator does not understand the manufacture environment thoroughly. It is the major reason why they have continued building schedule manually. This paper introduces the development of scheduler based on simulation model considering flexible takt time and number of workstations to meet the due date in Make-to-Order system. Two types of products, the one is overhaul and the other is new product, are produced in the same shop.