An object of this invention is to generate NC (Numerical Control) data to improve efficiency of machining. This invention comprises the steps of: generating NC data to machine a first portion of an object, wherein the first portion is specified based on a supposed cutting load distribution of the object; and generating NC data to machine the object after the first portion of the object was machined. Thus, at least two-phase machining data is generated which is separated based on high or low of the supposed cutting load, for example. That is, a tool machine processes the object stepwise. Therefore, it becomes possible that a portion is machined in advance, that it is determined that it is better to machine beforehand based on the supposed cutting load distribution, and the object after the machining is separately machined.