PURPOSE: To assure the optimum machining control even when machining types such as rough finishing, semi-finishing and final finishing, etc., are continuously carried out by setting and storing previously the value of parameter which varies for each machining type and carrying out the machining program set for each machining type.

CONSTITUTION: The parameter value that should be varied in response to each machining type is previously set and stored in a memory 14 of an NC device 10. An operator sets the machining programs and the machining types corresponding to each other in the device 10 and defines a machining type for each machining program. The device 10 which has started to carry out the machining program, decides the machining type of the machining program to be carried out according to the corresponding relation between the set machining program and machining type. Then, the device 10 changes the parameter value to change the setting into the parameter value stored in the memory 14 in according with each machining type and carries out the relevant machining program.