PURPOSE: To detect abnormality at the time of working from the side of workpiece at an early time by providing a table to which the workpiece is fixed, at a DD motor, and detecting the cutting resistance upon drilling on the basis of torque generated by the motor.

CONSTITUTION: When the cutting resistance upon drilling becomes large, the rotary moment applied to a table 2 increases, while a control part 6 increases excitation current supplied to a DD motor 51 to perform control so as to make torque large. Torque detection means 8 detects torque generated by the motor 51 form the excitation current supplied form a drive circuit 7. Cutting resistance detection means 9 detects the cutting resistance from the torque detected. When the cutting resistance detected exceeds a reference value, force applied to a workpiece is too large and to cope with it, a control signal is sent to a feed means 4 to make the feed speed of drill delay. Abnormality upon working is detected at the side of the workpiece to control the operation of drill in this way.