Abstract: A numerical control apparatus for machine tool, includes an NC program storage portion for storing an NC program; a transformer means for performing an optimizing process for analyzing the NC program and parameters in the machine tool and transforming the NC program in an optimum condition; an optimized program generated by said transformer means and containing an optimized main program, and optimized data; first and second optimized data storage portions for storing and holding the optimized data. While the machine tool is operated according to the optimized program on the basis of the optimized data stored in the first optimized data storage portion, the transformer means can generate new optimized data on the basis of the NC program and can write a transformed data in the second optimized data storage portions.