PURPOSE: To carry out a magnetic grinding well and automatically even to a member to grind which has a complicated surface form such as recesses.

CONSTITUTION: While a grinding head 10 is moved in three-dimensional directions by a three-dimensional moving device according to the moving locus data preset according to the surface form of a member to grind, the first arm 22 is rotated around the axis of the grinding head 10, and the second arm 50 is rotated around the axis of a rotary shaft 48. As a result, the member is ground magnetically automatically following the surface, in the condition that the top face 80 of a spindle magnetic pole 52 driven to rotate around the axis by a driving motor 20 is opposed to the surface of the member to grind.