To provide a grinding device and a grinding method for easily forming a super-semispherical concave surface.

An oscillating mechanism 57 rotates a grinding wheel part 10 around the oscillating center PC arranged inside an opening OP, and a super-semispherical concave surface SS deeper than a semispherical concave surface can be easily worked in a workpiece WP to be ground. In other words, the oscillating center PC of the grinding wheel part 10 corresponds to the center of curvature of the concave spherical surface, and the arrangement of the oscillating center inside the opening OP means that the super-semispherical concave surface SS inside the opening OP can be ground.