PURPOSE: To make it possible to correct a backlash quantity irrespective of a lost motion quantity by reading a value B on a displacement detector when a driven body is located in a position A, and reading a value B' on the detector when the driven body is retreated after its advance and returned to the position A, so that B-B' is regarded as a backlash quantity and corrected.

CONSTITUTION: When a + direction positioning command and a positioning speed command within the measuring range of a displacement detector 9 are input into a servo controller 11, the controller 11 outputs a drive command to a servo motor 7 so as to rotate it, and the detector 9 inputs the current value in a located position to a NC device 12 one after another, so that a position A at the completion of positioning is read and memorized, on the other hand, the NC device 12 outputs a reading command to the detector 9 at the completion of positioning, so that a detected value B is read and memorized. And then, the device 12 slightly shifts a table in + direction, and it reverses the table so as to locate it in the position A in the opposite direction. And the device 12 outputs a reading command to the detector 9 so that a detected value B' is read and input therein. Then B-B'=C is computed in the device 12, and the previous correction value is renewed where the value C is a backlash quantity, and the renewed correction value is adopted from the input of a following positioning command.