In writing an NC program for controlling the machining of a workpiece by a machine, information required for the machining quality by the machine is included. The NC program is analyzed, and a measurement program for measuring the machining quality of the workpiece by means of a measuring instrument is written. The machining quality of the workpiece is measured by means of the measurement program and the measuring instrument. The results of the measurement are checked with the information on the machining quality included in the NC program to judge the machining quality of the workpiece. By using the judgment on the quality, when a system such as a CIM (Computer Integrated Manufacturing) is build up in cooperation with another machine, the system control is simplified and made efficient.