PURPOSE: To perform a quick and stable emergency return, by providing a zero detecting means of a deviation amount between a feedback signal and an instruction signal and an emergency return instruction enable means performing an emergency return only when said zero detecting means detects zero.

CONSTITUTION: If a deviation value SD becomes zero, a zero detection signal C4 is output to an AND gate G7 from a comparator 31, and a gate G9 is opend. Then an emergency return instruction signal SB is set enable, consequently an FF33 is set, and an AND gate G11 is opened then a pulse signal P is output to a down count terminal DN. Accordingly, a DC motor 7 is once stopped by the deviation amount SD becoming to zero, and then reversely rotated at a high speed by a deviation amount SD- between a number of pulses of the signal P and a number of pulses of a feedback pulse signal FP- from a rotation selector circuit 20, while a saddle 4 mounting a main spindle 1 is quickly returned, and as a signal R is output if a dog 12 taps a switch 11, the FF33 is reset, and the gate G11' is closed then the signal P is disconnected finally a main spindle 1 is stopped at the original point.