Simulation of railways control and protection systems allows the performance of different research tasks at low cost. The possibilities range from the design of the overall system to the planning of the allocation of trackside equipment, checking their influence over the line movements. In this case, simulation of ERTMS / ETCS (European Rail Traffic Management System / European Train Control System) system is especially interesting for its novelty. One properly design simulator would allow to check the technical specifications for finding contradictions that may be introduced during the design of the system, and their subsequent correction. Employment of the simulator for the implementation of the driving and circulation rules is possible too. One simulator would definitely be the essential tool for the final step between the design and the implementation of ERTMS / ETCS. In this paper, one ERTMS / ETCS simulator is presented. This tool is developed under Visual C++, using the power of Object Oriented Programming, and is organized in several applications, which communicates each other by means of the CORBA standard. System Requirements Specifications written by the members of the UNISIG group are fulfilled. Any line configuration in order to reproduce different scenarios is allowed. In this way exercises may be run in the simulator to obtain information about the system and reach the objectives listed above. In the simulator, different equipments of the ERTMS / ETCS system are clearly separated in trackside and trainborne equipments. In the trainborne