In the painting process in automotive manufacturing, the repair polishing process is still done manually by a worker with a sufficient skilled technique. However, the number of skilled workers is decreasing with the aging. In addition, the polishing time and the surface quality after the repair polishing are dependent on the proficiency level of the worker. Thus, skill-independent automation technology for the repair polishing is required. In our past research, the serial-parallel mechanism polishing machine was developed for automating the polishing process. The developed machine can control the tool trajectory, tool posture and polishing force simultaneously. In addition, the polishing force is controlled without external sensors by the reaction force observer system. This study aims to develop a polishing automation method for unknown 3- dimensional curved surface by using the developed machine. First, the tool posture control method on unknown curved surface was proposed. Second, the normal force control method based on the posture information was proposed. By using these proposed methods simultaneously, the tool posture and polishing force were controlled in the normal direction on unknown 3-dimesional curved surface. From the experimental results, the validity of the proposed method was verified.