A polished-piece holder is provided that does not easily stick or adsorb to a polishing pad of a polishing apparatus and reduces occurrences of production line troubles and therefore the number of failed polished pieces. A single sheet of a thermosetting resin impregnated fiber substrate or a laminated sheet formed by laminating a plurality of sheets of the thermosetting resin impregnated fiber substrate is formed under heat and pressure into a plate. The thermosetting resin impregnated fiber plate is then processed to form a polished-piece holder for holding pieces to be polished. The evaluation portion has a certain length in a direction of the average line. The thermosetting resin impregnated fiber plate has a surface roughness with a maximum wave height Ry of 10 .mu.m or greater over an almost entire area of the surface layer. The maximum wave height Ry is determined in an evaluation portion of a wave curve by summing a height Rp of a highest crest and a depth Rv of a deepest trough from an average line of the wave curve. The wave curve is taken from a cross-sectional curve obtained by the surface roughness measuring device.
A glass substrate for a data recording medium is manufactured by using a tabular carrier with circular holes formed therein, housing disk-shaped glass workpieces in the circular holes of this carrier, sliding polishing pads over the surface of the carrier and the principal surfaces of the glass workpieces and polishing the glass workpieces until the height (NRa) of micro-waviness on the principal surfaces of the glass workpieces is reduced to a predetermined value or less. The height (NRa) of micro-waviness of the principal surfaces is a value dependent on the surface roughness of the polishing pad and the surface roughness of this polishing pad is a value dependent on the surface roughness of the carrier. A glass substrate for a data recording medium is manufactured by reducing the surface roughness (Ra) of the carrier to 0.08 .mu.m or less and polishing the glass workpieces until the height (NRa) of micro-waviness on the principal surfaces measured using a three-dimensional surface structure analysis microscope whose measuring wavelength (.lambda.) is set to 0.2 to 1.4 mm is reduced to 0.12 nm or less.
