A main control process is made common to all machine tools by describing in a NC program a tool trajectory including a change in posture in a coordinate system (30) fixed to a machining object (W), fixedly arranging a preparatory reference coordinate system (20) on a machine table (2), representing an installation position of the machining object (W) and a position of a spindle (91) on which a tool (11) is mounted in the preparatory reference coordinate system (20), and containing portions relating to a configuration of axes in a conversion function group of correlation between the position (q) of the spindle (91) and an axis coordinate (r). Thus, the processes of reading the NC program, correction of the tool trajectory and conversion into the trajectory of a spindle position based on the installation position of the machining object, the tool shape, and tool dimensions are made completely common.