Abstract: A tool posture control system according to the present invention rotates a tool vector v.sub.1 indicative of a present tool position to a target tool vector v.sup.1 through vector rotation, and generates data for driving robot axes from the data produced by the vector rotation. For a welding robot, for example, the inclination of a torch with respect to an arc starting surface can automatically and appropriately be established, so that an arc starting point can accurately be searched for. Therefore, the operation to search for a desired arc starting point can properly be carried out without human intervention.