PURPOSE: To prevent a grinding stone from collision with a workpiece by calculating the rotation angle of a grinding stone table based on a grinding stone information table stored in a memory means in relation to a grinding stone selected by a selecting means, and positioning the grinding stone table to the calculated rotation angle of the grinding stone table.

CONSTITUTION: A grinding stone information table, e.g. the grinding stone angle of the rotary shaft of the grinding stone and a main spindle with a grinding stone, is set by a setting means 35, and the grinding stone information table set by the setting means 35 is stored in a memory means 36. A desired grinding stone information table is selected by a selecting means 28, and based on a selected grinding stone information table stored in a memory means 36, the rotation angle of the grinding stone table is calculated by a computing means 32. A drive means 13 is then controlled by a control means 34 so that the grinding stone table is positioned to the rotation angle of the grinding stone table calculated by the computing means 32.