PURPOSE: To cut a thread having a high degree of accuracy which is not affected by the number of pulses and the lead of a spindle by carrying out computation including the distance which is obtained by subtracting the distance of a shift that is from the initiation point of each of threads during multi-thread cutting, from an accumulated moving distance when the accumulated moving distance exceeds the distance of shift.

CONSTITUTION: A reading section 2 reads an instruction value while an analyzing section 3 computes a feed amount SA per pulse which is then stored in a thread cut function generat ing and control section 7 and a computing section 12, and the distance SF of a shift from the initiation point of each of multi-threads is computed and is stored in a comparing section 11. The reading section 6 reads the number SC of pulses corresponding to the rotational speed of a spindle 4 and an one revolution reference signal SD from a pulse generator 5, and the thread cut function generating section 12 initiates computation using the signal SD as a starting signal so that the distance SG of movement is delivered to the comparing section 11 in accordance with the feed amount SA and the number SC of pulses. When the distance SG of movement exceeds the distance SF of shift, the control section 7 generates a function in accordance with the feed amount SA and the number SC of pulses, and therefore, the threads are cut using desired values including the distance which is obtained by subtracting the distance SF of shift from the distance SG of movement.