To reduce chamfering cost and material cost by making shallow the depth of a chipping produced while chamfering a glass disk.

The peripheral speeds of an inside diameter chamfering grinding wheel 3 and an outside diameter chambering grinding wheel 4 are respectively within the range of 1200 to 10000 m/min and the peripheral speed ratio of the inside chamfering of a glass disk 1 to that of the inside diameter chamfering grinding wheel 3 and the peripheral speed ratio of the outside diameter chambering of the glass disk 1 to that of the outside chambering grinding wheel 4 are both within the range of 1/10 to 1/100.