To mass-produce discs polished at a high accuracy by assembling a ring like polishing member rotary polishing device as a unit of a system.

Ringlike polishing member rotary polishing devices 3-1, 3-2 perform the R-working to both surfaces of a disc D1 so as to improve the degree of flatness. When working of the disc D1 by a polishing device 1 and supply of a following disc D2 by a disc supplying device 2 are concluded, the disc D1 is positioned at a washing position of a washing device 4. After washing of the disc D1, working of the disc D2 and supply of a disc D3 are concluded, the disc D1 is positioned to a polishing position of a polishing device 6. Ringlike polishing member rotary polishing devices 6-1, 6-2 are moved to the disc D1 side so as to perform the C-working to both surfaces of the magnetic disc D1. Namely, since the C-working is performed to the disc D1 having a high degree of flatness, polishing at a high accuracy is obtained.