To cut a disk pattern by an edge of a coring grinding wheel by detecting mechanical coordinates based on alignment marks formed on a glass pane.

This machining method for the encoder glass disk is so formed that the glass pane 1 sticking with an ultraviolet hardening tape 10 is mounted on an absorbing stand 12, the mechanical coordinates of the disk pattern 2 are determined by reading the alignment marks 11 on the glass pane 1 by a CCD camera 15, and the edge 17 of the coring grinding wheel cuts it to provide the glass disk.