Provided is a correction data checking system, for robots, which makes it easy to reveal the cause of a machining defect. A laser machining head and a distance sensor or a sensor for detecting a work line are attached to the distal end of a robot arm. A robot is driven based on a teaching program, and a copying control technique is implemented based on information sent from the sensor so that the distance between the laser machining head and a workpiece will be equal to a set value. A path of taught positions of the laser machining head and a path of actual positions thereof are displayed in comparison with each other on a display of a teaching console or the like. Moreover, the difference between the taught position and actual position is calculated and displayed. As both the position commanded by the teaching program and the actual position derived from the copying control technique are displayed, if a machining defect occurs, the machining defect is checked to see if it is a problem attributable to the sensor or a problem attributable to the workpiece or a jig. The cause of the machining defect is then revealed. Consequently, the cause of a machining defect can be quickly revealed and dealt with at a working site.