A cast metal is generally produced by using a sand mold. A foamed polystyrene mold is used as the master mold for making the corresponding sand mold. Recently, the development of a flexible machining robot for foamed polystyrene materials is expected in the cast metal industries because of the high cost and inefficiency of conventional large-sized CNC machine tools. In this paper, a machining robot based on an industrial robot is proposed for foamed polystyrene materials. A compact and light weight tool is developed and attached to the arm tip. Also, the robot has a novel robotic CAM system from the view point of teachingless operation. The proposed CAM system performs the basic function which enables the robot arm to follow not only numerical control data (NC data) but also cutter location data (CL data) consisting of position and normal direction vectors. The developed robotic CAM system provides a simple interface without using any robot languages between a well-known CAD/CAM system and the robot arm RV1A. The basic design of the machining robot using the robotic CAM system is presented for foamed polystyrene materials.