To provide a method of processing a hard substrate so that when an optical device layer is laminated on the surface of the hard substrate thereafter the optical layer has a flat surface.

The method of processing a hard substrate is performed as the followings. In a first step, a positional relationship between a chuck table and a grinding wheel is set so that while an annular grinding stone passes over a rotation center of the hard substrate held on the chuck table, the grinding is started from the rotation center of the hard substrate, then the concentric grinding gradually stretches out to the outer periphery. In the next step, while the grinding wheel is rotated, the grinding stone comes in contact with the rotation center of the hard substrate held on the chuck table, then the grinding is started from the rotation center of the hard substrate, and the grinding wheel is fed so that the concentric grinding gradually stretches out to the outer periphery, so that a top surface of the hard substrate is ground in a concave shape in which the height gradually increases from the rotation center towards the outer periphery.