A method for evaluating a toolpath traveled by a rotating tool when the rotating tool machines a workpiece while moving relative to the workpiece, including: a calculation step for, based on a predetermined target toolpath and the shape of the workpiece before the workpiece is machined by moving the rotating tool along the target toolpath, calculating the dimensions of a contact area of the bottom surface portion of the rotating tool where the bottom portion is predicted to be in contact with the workpiece when the workpiece is actually machined by moving the rotating tool along the target toolpath, said bottom surface portion intersecting the rotational axis line of the tool; and a determination step for determining that the target toolpath is inappropriate if the dimensions of the contact area exceed predetermined threshold values when the rotating tool is positioned at any location along the target toolpath.