PURPOSE: To make the unattended continuous operation of a machine tool possible by controlling tool relief and its return to an original position to reduce a load according to output given by a detecting means of the case in which adaptive control becomes impossible and a tool position storage means.

CONSTITUTION: The cutting horsepower 19 of a main motor 1 detected by a detector 2 is compared with a target horsepower 20 in a cutting speed computing section 11, and when it is reduced to a horsepower corresponding to the minimum set value of feed speed, but does not decrease to the target horsepower 20, adaptive control is detected as impossibility, and a tool relief and return control section 13 stops therefore the feed of a motor 15 through a tool position control section 18. At the same time, the information 22 of preset tool position indicated by a tool position detecting section 17 is keept in a machining position storage section 12. Nextly, the control section 13 controls a motor 16 to make the tool to clear a fixed distance α, and then causes the tool to cut a part being in front of the final point of the cleared distance α. When that cutting work has been completed, the tool is returned to the starting point of the cleared distance α kept in the strage section 12 to continue the last lap cutting as far as the distance α. Thus the unattended continuous operation of a machine tool can be easily realized.