Abstract: A control device of a machine tool (100) has an input unit (1) for inputting the processing profile data (1a) and the workpiece data (1b) of the material and a profile of the workpiece to be processed. The control device input unit (1) also can receive a tool path changing operation command (1c), a manual operation command (1d) and a processing condition changing command. A data base (3) for storing at least one of the mechanical data of the machine tool to process the workpiece and the tool data of the tool mounted on the machine tool provides a signal to an estimating calculation unit (7) for estimating at least a processing load or the occurrence of interference of the tool with the workpiece based on the data inputted by the input unit (1) and the data stored in the data base (3).