Research Question This study focused on the Computer Integrated Manufacturing (CIM) of a manufacturing company producing precast concrete products using a simulation technique. CIM integrates information among segments of marketing department, manufacturing department and warehouse department. In this study, we use a virtual company (MKS Company) producing precast concrete products as the company will be sustainable if it can solve the problem of critical path. Internet of Things (IoT) can contribute to shortening the path by communicating and thus sharing information in each department simultaneously. The result of simulation shows the cost performance of IoT is positive. Market Department collects client information and market information. The collected information is gathered together and is forwarded to Manufacturing Department. Plant manager issues a job order. As MSK must a manufacturing products by Make to Stock method. The job order must be based on the correct market information. With IoT enables MSK to make a correct estimation of the necessary quantity of production. MSK can minimize the Opportunity Loss and Unsold Product Loss. On the other hand, MSK must be patient to suffer a large amount of Opportunity Loss in case of Without IoT. Simulation shows that MSK can decrease almost 90% of Loss by IoT.