To suppress the deformation of the peripheral edge of a wafer and to prevent a failure such as the over polishing of the wafer caused by the deformation.

In a polishing head 13 polishing the wafer W pressed against a polishing pad 16 thereof, the reinforcement member 22A of circular shape in a plan view whose inner diameter is substantially equal to the diameter of the wafer W is applied to the top surface of the wafer W with the adhesive 21. The reinforcement member 22A is formed in a substantially inverted dish shape (or in a flat plate shape), and the wafer W is engaged to the inside of the reinforcement member 22A. Polishing the wafer W attached to the reinforcement member 22A helps suppress the buckling distortion and the like of the peripheral edge of the wafer W caused when the wafer W comes into contact or collision with the retainer ring 19 while it is being polished.