PURPOSE: To adjust the range of reciprocating a table secured thereto with a cutting tool, to a minimum necessary value so as to efficiently polish the workpiece by controlling the reciprocating range with reference to a position where a detecting bar makes contact with a reference condition detecting switch.

CONSTITUTION: The center of a cutting tool 10 is positioned at a setting mark 6P formed on a tool bed 6 fixed to a table 2. When a reference condition detecting switch 8 detects a detecting bar 20, a reference condition detection signal for the table 2 is generated. Further, when the detecting bar 20 is detected by an initial position detecting switch 5, an initial position detection signal is generated. Further, the table 2 is reciprocated in opposite directions so as to polish at first a grinding wheel 11K. That is, the grinding wheel 11K is rotated, and is lowered (90), and then, after it is elevated (91), the rotation is stopped. Next, the grinding by the grinding wheel 12K is operated. Then, the table 2 is returned to one end of a rail, and is stopped.