In the painting process of automotive manufacturing, the buffing process for the repair polishing is done manually by a worker with a sufficient skilled technique. However, the number of a skilled worker is decreasing with the aging of the skilled worker. 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 to control the tool trajectory, tool posture and polishing force simultaneously. Moreover, a skilled buffing technique was acquired from the skilled worker and the skilled buffing technique was replicated on the flat surface with the use of the developed machine. This study aims to develop a polishing method for unknown curved surface by controlling the tool posture and polishing force in the normal direction to the surface. From the buffing experimental results, the tool posture and polishing force were controlled in the normal direction on unknown curved surface accurately. Finally, by using the developed control method on unknown curved surface and the buffing replication method, the skilled buffing technique was replicated on the unknown curved surface.