A reference direction of the correction of the torch of a robot (1) is defined. A correction direction suitable to robot control is calculated on the basis of the definition and the moving direction of the robot (1) using the correction direction information specified through a man-machine interface (200) for directing the correction direction to be changed. An algorism is provided to calculate a correction amount in the correction direction for each predetermined interpolation sampling and to add it during robot interpolation. Thus, a sensor correction direction can be changed in real time while the robot operates. This permits the distortion of a work to be always dealt with suitably to provide an accurate correction operation.