This article presents a model conversion approach to developing a 3D discrete event system specification (DEVS)-based factory simulator, in which the target automated manufacturing systems (AMS) are modeled by employing a job-resource relation network (JR-net), and this input JR-net model is systematically converted to a DEVS model. For this purpose, the JR-net modeling framework has been extended further to handle 3D geometric information while providing a formal specification of the JR-net. Also, a hierarchical DEVS model architecture and a systematic conversion method for converting a JR-net model into a DEVS model are proposed. Based on the proposed approach, a 3D factory simulator has been developed in C++ with OpenGL and a DEVS engine. The proposed factory simulator may be used as a virtual prototyping tool for designing new AMS. Its validity is demonstrated by constructing a virtual factory of a special type of AMS called a flexible manufacturing system.