1. An intelligent machining system for automatically determining machining conditions and for controlling a numerically controlled machine tool to machine a workpiece in accordance with the machining conditions, said intelligent machining system comprising: attribute data storage means for storing attribute data indicating characteristics of at least one of said workpiece and machining requirements; and machining condition calculating means for calculating the machining conditions on the basis of the attribute data, said machining condition calculating means comprising: reference value calculating means for calculating reference machining conditions on the basis of the attribute data by the use of predetermined calculating expressions; and a first neural network responsive to the attribute data and associated with said reference value calculating means so that the reference machining conditions calculated by the reference value calculating means are corrected by said first neural network so as to output the corrected machining conditions from said machining condition calculating means to said machine tool to machine said workpiece.