The present invention provides a numerically controlled machine tool and a program transforming method therefor where a NC program is transformed into an optimum program even by a non-expert programmer. Particularly, the present invention provides a method for optimizing a NC program for operating a numerically controlled machine tool, comprising: making the NC program to be loaded into the numerically controlled machine tool; designating a portion of the NC program to be determined whether it is transformable and/or a portion of the NC program to be determined whether a command position is changeable; storing the NC program in a memory; determining whether the designated portion is transformable and/or whether the designated command position is changeable; and transforming the designated portion and/or changing the designated command position, and making an operating program file for the numerically controlled machine tool.