PURPOSE: To enable a copying operation to be continued from a certain past point by taking in a copying operation in a machine coordinate position for each sample period and storing it in a memory, and moving back to a position corresponding to said certain past point in said memory when an abnormal copying is detected.

CONSTITUTION: When a comparing circuit 4 has detected and abnormal copying, such as, a stylus 3 has been off from a master 2 and jumped or caught in the recessed part of the master 2 and the like the copying operation is one stopped. After that, the operation is moved back to a machine position corresponding to the earliest position in the memory 15 by means of an NC feed, from which the copying operation is resumed again. As for copying data, those from the backed machine position to the position in which an abnormal copying is detected, are discarded, and new data to be obtained after resuming are arranged to be smoothly connected to data before those which are discarded. In resuming, it is possible to carry out copying at a low speed during a certain section, and to increase the speed to a set copying speed, to continue the copying operation.