a workpiece holding device enables stable polishing to be performed without sacrificing the structural strength of a top ring or the space necessary for machining a through hole or implanting engaging pins while allowing close contact to be made between a workpiece to a polishing cloth on a polishing tool . the top ring includes a top ring member having a holder plate for holding the workpiece on a front surface and a cover plate attached to a back surface of the holder plate by engaging a depression section formed on a back surface of the holder plate with a protrusion section formed on a front surface of the cover plate . a curved surface bearing unit provided between an end portion of a drive shaft and a back surface of the cover plate couples the drive shaft and the top ring member while permitting motion of the top ring member relative to the polishing tool . at least a portion of the curved surface bearing unit is positioned within the depression section .