In this study, the prototype of a system for checking risk-factor of NC machine is proposed. The proposed system can get the risk-related information by monitoring the status of real-time processes of NC machines. Using the information, the accidents can be prevented by the background process of an expert system tool. This paper consists of 2 parts: (1) the method for gathering data and definition of the risk-related factors of NC machines and (2) the procedure for finding the proper actions by using the forward chaining of a rule-base. Proposed system is implemented with C++ language under MS-windows.