To prevent the butt section of a polishing pad from peeling and elongation in mirror machining.

This device is provided with a drum body 30, which rotates around the center axis 10a and a polishing pad 31, which is affixed to the peripheral face of this drum body 30 and mirror machines the edge of a wafer W. Concretely, the polishing pad 31 is stuck to the drum body 30 in such a way that a butt section 32 comprising end faces 33 and 34 butted is inclined at an angle of θ to a rotation direction A. This angle θ is desirable to be set at an angle ranging from 45° to 60°.