To eliminate occurrence of shape degradation or work decomposition layer of a semiconductor device.

A dummy ring 14 is pressed against a polisher 4 by an air cylinder of a coarse movement Z table. A semiconductor device 26 is so pressed by an air cylinder 22 as to be positioned on the same polisher surface before starting polishing, and under the state, the air cylinder 22 is air-locked to fix an upper and lower positions of the semiconductor device 26. During polishing process, only the semiconductor device 26 is polished while the dummy ring 14 polished little. As the polishing progresses, the semiconductor device 26 contacting to the polisher at first gradually shifts to non-contact state. At the non-contact polishing, an unevenness at a top surface layer part of the semiconductor device 26 which occurred at contact-state polishing is removed by etching.