Abstract: A machine tool includes a first motor that receives load fluctuation when the workpiece is processed and a second motor that operates to change the plural kinds of tools. An information processing device takes out the current of the first motor measured by the first current sensor for each signal that occurs at the changing operation of the plural kinds of tools and is measured by the second current sensor, and relatively compares a non-negative function value that has a current value at each taken-out segment as a parameter for each number of times of processing on the workpiece, thereby detecting a tool abnormality for each kind of the tool.